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Fiber Installation and Activation | Fiberinstall.pdf |
Fiber Installation and Activation Credits and Copyright We would like to thank: © 2023 Jones/NCTI, Inc. Jeff Hecht, Rob Meives, Kathleen Maiman, Dwight Miller, Steve Rounds, and Chris Walden 3M Communication Markets Division, Adtran, Inc., AFL, Alpha Technologies, American Polywater Corp., ARRIS, Aurora Networks, BP enterprises, BT Research, Charles Industries, Comcast Corp., Commscope Inc., Condux International Inc., Corning Cable Systems, FS. com Inc., Force, Inc., Hi-Tool Co., Institute of Electrical and Electronics Engineers Inc., Jet Line Division/Thomas Industries Inc., Jonard Tools, The Light Brigade Inc., Lightel Technologies, NC Power Systems, Norland Products, PD-LD, Inc., Point Broadband, Sorrento Networks, Steward & Stevenson Power Inc., TE Connectivity, TC Communications, UCL Swift, Verità Telecommunications Corporation, Viavi Solutions Inc., and Xtera Jeff Gibson, Annamarie Gilbert, Von Mc Connell, Tyler Newberry, Shaun Pearson, Jonica Rich, Kendall Robinson, James Scherz, Donna Urban, and Susan Yao Li | Fiberinstall.pdf |
Contents at a G lance LESSON 1: FIBER-OPTIC TECHNOLOGY (68 0-10-7) LESSON 2: FIBER-OPTIC CABLE PROPERTI ES (680-20-6) LESSON 3: INTRODUCTION TO FIBER-OPTIC NETWORKS (680-15-6) LESSON 4: FIBER-OPTIC NETWORK DESIGN (680-50-6) LESSON 5: FIBER-OPTIC NETWORK ARCHIT ECTURES AND TOPOLOGI ES (680-42-4) LESSON 6: PASSIVE OPTICAL NETW ORKS (680-60-4) LESSON 7: OPTICAL TRANSMISSION SYSTEMS (680-40-7) LESSON 8: OPTICAL SIGNAL TRAN SMITTING AND RECEIVI NG (680-45-7) LESSON 9: FIBER-OPTIC CABLE CONSTRUC TION TECHNIQUES (680-35-5) LESSON 10: FIBER-OPTIC NODE POWERING (680-55-5) LESSON 11: OUTSIDE PLANT FIBER-OPTIC CABLE INSTALLA TION (680-37-3) LESSON 12: FIBER-OPTIC COMPONENTS AND T ERMINATIONS (680-25-6) LESSON 13: FIBER-OPTIC CABLE SPLICING PREPARATION (680-30-4) LESSON 14: FIBER-OPTIC CABLE SPLICING AND TERMINATING (680-32-3) | Fiberinstall.pdf |
Fiberinstall.pdf |
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Fiber Installation and Activation Page 1 LESSON 1: FIBER-OPTIC TECHNOLOGY (68 0-10-7) FIBER-OPTIC TECHNOLOGY BAS ICS Introduction to Fiber-Optic Technology Basics ............................................................................. 2 Advantages of Fiber Optics ............................................................................................................ 2 Industry Standards Organizations ................................................................................................ 4 Electromagnetic Spectrum and Wavelength ................................................................................. 5 Basic Fiber-Optic Communications Networks ............................................................................... 8 Optical Fib er Basics ....................................................................................................................... 9 LIGHT SOURCES Introduction to Light Sources ...................................................................................................... 13 Light Source Selection Factors ..................................................................................................... 13 Laser Diodes ................................................................................................................................. 15 Light-Emitting Diodes .................................................................................................................. 21 Optical Modulation ....................................................................................................................... 22 OPTICAL RECEIVERS Introduction to Optical Receivers ................................................................................................ 25 Performance Criteri a for Optical Receivers ................................................................................. 25 PIN Diode Optical Detectors ........................................................................................................ 28 Avalanche Photodiode Optical Detectors ..................................................................................... 29 Detection and D emodulation ........................................................................................................ 31 LESSON 2: FIBER-OPTIC CABLE PROPERTI ES (680-20-6) OPTICAL FIBER TYPES Introduction to Optical Fiber Types ............................................................................................. 34 Fiber-Optic Basics ........................................................................................................................ 34 Single-Mode Fiber ........................................................................................................................ 35 Dispersion Shifting in Single-Mode Fiber.................................................................................... 37 Variations of Standard Single-Mode Fiber .................................................................................. 41 Multimode Fiber ........................................................................................................................... 43 FIBER PERFORMANCE Introduction to Fiber Performance .............................................................................................. 45 Optical Attenuation ...................................................................................................................... 45 Refractive Index ........................................................................................................................... 48 Total Internal Reflection .............................................................................................................. 49 Fresnel Reflections ....................................................................................................................... 50 Light Dispersion ........................................................................................................................... 51 OPTICAL FIBER DIMENS ION TOLERANCES Introduction to Optical Fiber Dimension Toleran ces.................................................................. 57 The Core and Mode Field Diameter ............................................................................................. 57 Cladding Dimensions ................................................................................................................... 60 Dimension Tolerances When Splicing .......................................................................................... 61 Optical Fiber Coatings ................................................................................................................. 64 Ribbon Fibers ................................................................................................................................ 65 | Fiberinstall.pdf |
Fiber Installation and Activation Page 2 LESSON 3: INTRODUCTION TO FIBE R-OPTIC NETWORKS (680-15-6) BASIC HFC ARCHITECTU RE Introduction to Basic HFC Architecture ...................................................................................... 70 The Headend ................................................................................................................................. 70 Headends and Hubs ..................................................................................................................... 73 OPTICAL NODES Introduction to Optical Nodes ...................................................................................................... 81 Optical Node Overview ................................................................................................................. 81 Scalable Node Configuration Options .......................................................................................... 83 Status Monitoring......................................................................................................................... 85 Digital Return Path Transmission ............................................................................................... 86 FIBER-OPTIC NETWORK S ERVICES Introduction to Fiber-Optic Network Services............................................................................. 89 Video Signal Acquisition .............................................................................................................. 89 Carrying Voice Signals ................................................................................................................. 90 Sending and Receiving High-Spee d Data .................................................................................... 92 Video-on-Demand ......................................................................................................................... 95 Channel Lineup Customization ................................................................................................... 97 Advertising Insertion Capability ................................................................................................. 97 HFC Network Connectiv ity to the PSTN and the Internet ......................................................... 98 FIBER TRANSMISSION S TANDARDS Introduction to Fiber Transmission Standards ........................................................................... 99 Fiber-Optic Transmission Systems .............................................................................................. 99 SONET, Ethernet, and OTN ...................................................................................................... 101 FIBER SAFETY Introduction to Fiber Safety ....................................................................................................... 103 Handling Fiber in a Safe Work Environment ............................................................................ 103 Protective Eyewear ..................................................................................................................... 105 Chemicals in the Fiber-Optic Workplace ................................................................................... 105 Fiber-Optic Cleanliness .............................................................................................................. 106 LESSON 4: FIBER-OPTIC NETWORK DESIGN (680-50-6) NETWORK DESIGN GUIDE LINES Introduction to Network Design Guidelines .............................................................................. 110 Network Usage ........................................................................................................................... 110 Network Design .......................................................................................................................... 114 Network Design with Limited Resources .................................................................................. 117 NETWORK DESIGN ROUTE Introduction to Network Design Route ...................................................................................... 119 Fiber-Optic Route and Design Map ........................................................................................... 119 Splice Closure Locations ............................................................................................................ 122 Slack Loop Design ...................................................................................................................... 124 Franchise Agreements ................................................................................................................ 126 NETWORK DOCUMENTATIO N Introduction to Network Documentation ................................................................................... 129 Power Budgets and Total Link Loss .......................................................................................... 129 | Fiberinstall.pdf |
Fiber Installation and Activation Page 3 Acceptance Testing ..................................................................................................................... 132 Optical Network Documentation ............................................................................................... 134 As-Built Documentation ............................................................................................................. 137 LESSON 5: FIBER-OPTIC NETWORK ARCHIT ECTURES AND TOPOLOGI ES (680-42-4) FIBER-OPTIC NETWORK ARCHIT ECTURE Introduction to Fiber-Optic Network Architecture.................................................................... 140 Communications Network Architecture .................................................................................... 140 Network Architecture and Topologies........................................................................................ 141 Categorizing Netw ork Topologies .............................................................................................. 142 Common Fiber-Optic Network Topologies ................................................................................. 143 FTTX NETWORKS Introduction to FTTx Networks ................................................................................................. 149 Fiber-Optic Cable Installations in a Broadband Network ........................................................ 149 FTTx Topologies ......................................................................................................................... 151 PASSIVE OPTICAL NETW ORKS Introduction to Passive Optical Networks ................................................................................. 155 Passive Optical Network Overview ............................................................................................ 155 Fiber-Optic Cable in a PON ....................................................................................................... 156 PON Topologies .......................................................................................................................... 159 LESSON 6: PASSIVE OPTICAL NETW ORKS (680-60-4) PASSIVE OPTICAL NETW ORKS Introduction to Passive Optical Networks ................................................................................. 164 Passive Optical Network Access Architectures ......................................................................... 165 Passive Optical Network Wavelengths ...................................................................................... 166 Passive Optical Network Elements ............................................................................................ 169 PON ARCHITECTURES IN BROADBAND CABLE NETW ORKS Introduction to PON Architectures in Broadband Cable Networks .......................................... 179 Radio Frequency over Glass ....................................................................................................... 180 DOCSIS Provisioning of EPON .................................................................................................. 182 NEXT-GENERATION ACCESS Introduction to Next-Generation Access .................................................................................... 185 Next-Generation Access Architecture Requirements ................................................................ 186 XG-PON Architectures ............................................................................................................... 188 10G-EPON Architecture ............................................................................................................. 189 Point-to-Point Access Architectures ........................................................................................... 193 LESSON 7: OPTICAL TRANSMISSION SYSTEMS (680-40-7) OPTICAL MODULATION T ECHNIQUES Introduction to Optical Modulation Techniques ........................................................................ 198 Optical Modulation System Components ................................................................................... 198 Optical Modulation ..................................................................................................................... 199 Digital Modulation ..................................................................................................................... 204 | Fiberinstall.pdf |
Fiber Installation and Activation Page 4 Analog Modulation ..................................................................................................................... 207 OPTICAL DETECTION AN D DEMODULATION Introdu ction to Optical Detection and Demodulation ............................................................... 209 Direct Detection of Light Waves ................................................................................................ 209 Coherent Detection of Light Waves ........................................................................................... 210 Forward Error Correction .......................................................................................................... 212 WAVELENGTH DIVISION MULTIPLEXING Introduction to Wavelength Division Multiplexing ................................................................... 215 Wavelength Division Multiplexing ............................................................................................ 215 Wide Wavelength Division Multiplexing ................................................................................... 217 Coarse Wavelength Division Multiplexing ................................................................................ 218 Dense Wavelength Division Multiplexing ................................................................................. 219 Dispersion and DWDM ............................................................................................................... 222 LESSON 8: OPTICAL SIGNAL TRANS MITT ING AND RECEIVING (6 80-45-7) OPTICAL TRANSMITTERS Introduction to Optical Transmitters ........................................................................................ 228 Optical Transmitter Elements ................................................................................................... 228 Signal Processing ........................................................................................................................ 230 Optical Transmitter Lasers ........................................................................................................ 233 Optical Transmitter Levels ........................................................................................................ 235 OPTICAL RECEIVERS Introduction to Optical Receivers .............................................................................................. 237 Optical Receiver Elements ......................................................................................................... 237 Optical Receiver Power Levels ................................................................................................... 240 Optical Receiver Adjustment ..................................................................................................... 241 OPTICAL TRANSPORT EL EMENT S Introduction to Optical Transport Elements ............................................................................. 243 Optical Amplifiers ...................................................................................................................... 243 Optical Signal to Noise Ratio ..................................................................................................... 246 Optical Transponders and Repeaters......................................................................................... 248 Optical Signal Spli tting and Routing ......................................................................................... 249 Wavelength Division Multiplexing in the Optical Network ...................................................... 255 LESSON 9: FIBER-OPTIC CABLE CONSTRUC TION TECHNIQUES (680-35-5) SAFETY OVERVIEW Introduction to Safety Overview ................................................................................................ 260 Safety Codes and Safety Organizations ..................................................................................... 260 Construction Safety Practices .................................................................................................... 262 Aerial High-Voltage Hazards ..................................................................................................... 264 FIBER-OPTIC CABLE OUTSIDE PLANT INSTALLATION Introduction to Fiber-Optic Cable Outside Plant Installation .................................................. 265 Fiber-Optic Cable Installation Considerations .......................................................................... 265 Pulling Fiber-Optic Cable........................................................................................................... 270 Grounding and Bonding ............................................................................................................. 272 Storage Locations ....................................................................................................................... 273 | Fiberinstall.pdf |
Fiber Installation and Activation Page 5 LESSON 10: FIBER-OPTIC NODE POWERING (680-55-5) OPTICAL NETWORK POWE RING Introduction to Optical Network Powering ................................................................................ 278 Primary Power Sources .............................................................................................................. 279 Backup Power Sources ............................................................................................................... 283 OUTSIDE PLANT POWER DISTRIBUTION Introduction to Outside Plant Power Distribution .................................................................... 285 Centr alized Powering ................................................................................................................. 286 Distributed Powering ................................................................................................................. 288 NODE EQUIPMENT Introduction to Node Equipment ............................................................................................... 289 AC Voltage Ports ........................................................................................................................ 289 AC Power Distribution ............................................................................................................... 290 DC Power Supplies ..................................................................................................................... 292 FTTx Powering ........................................................................................................................... 293 LESSON 11: OUTSIDE PLANT FIBER-OPTIC CAB LE INSTALLATION (680-37-3) AERIAL FIBER-OPTIC CABLE INSTALLA TION Introduction to Aerial Fiber-Optic Cable Installation ............................................................... 296 Aerial Fiber-Optic Cable Installation Requirements ................................................................ 296 Aerial Fiber-Optic Cable Installation Techniques ..................................................................... 301 Fiber-Optic Cable Lashing ......................................................................................................... 305 Splice Closure Installation ......................................................................................................... 306 UNDERGROUND FIBER-OPTIC CABLE INSTALLA TION Introduction to Underground Fiber-Optic Cable Installation ................................................... 309 Conduit and Duct Overview ....................................................................................................... 310 Conduit Pulling Line .................................................................................................................. 312 Conduit Fiber-Optic Cable Installation ..................................................................................... 313 Fiber-Optic Cab le Jetting ........................................................................................................... 320 LESSON 12: FIBER-OPTIC COMPONENTS AND TERMINATIONS (680-25-6) OPTICAL CABLING STAN DARDS AND ELEMENTS Introduction to Optical Cabling Standards and Elements ........................................................ 324 Standardized Color-Coding Scheme ........................................................................................... 324 Fiber Coatings ............................................................................................................................ 325 Fiber-Optic Cable Structure ....................................................................................................... 326 Fiber-Optic Cable Types and Applications ................................................................................ 328 Ribbon Fiber ............................................................................................................................... 334 OPTICAL CONNECTORS Introduction to Optical Connectors ............................................................................................ 335 Optical Connector Components .................................................................................................. 335 Optical Return Loss and Reflectance ......................................................................................... 340 Cleaning Optical Connectors ...................................................................................................... 341 OPTICAL PATCH PANELS AND ANCI LLARY DEVICES Introduction to Optical Patch Panels and Ancillary Devices .................................................... 345 | Fiberinstall.pdf |
Fiber Installation and Activation Page 6 Patch Panels ............................................................................................................................... 345 FTTx Equipment ........................................................................................................................ 350 Ancillary Devices ........................................................................................................................ 351 Optical Fiber Pigtails ................................................................................................................. 353 Optical Splitters ......................................................................................................................... 354 LESSON 13: FIBER-OPTIC CABLE SPLICING PREPARATION (680-30-4) FIBER-OPTIC CABLE SPL ICING Introduction to Fiber-Optic Cable Splicing ................................................................................ 360 Splice Locations .......................................................................................................................... 360 Splice Closure Overview ............................................................................................................. 365 Safety in the Work Environment ............................................................................................... 366 SPLICE CLOSURES Introduction to Splice Closures .................................................................................................. 367 Fiber-Optic Cable Pre paration ................................................................................................... 367 Fiber-Optic Cable Protection ...................................................................................................... 369 Splice Closure Preparation ......................................................................................................... 370 Handling Closure Splice Trays .................................................................................................. 372 Splice Closure Completi on......................................................................................................... 378 LESSON 14: FIBER-OPTIC CABLE SPLICING AND TERMINATING (680-32-3) SPLICING TECHNIQUES Introduction to Splicing Techniques .......................................................................................... 384 Mechanical Splicing .................................................................................................................... 384 The Fusion Splicer ...................................................................................................................... 387 Fusion Splicing ........................................................................................................................... 391 Mid-Entry Splicing ..................................................................................................................... 397 Acceptance Testing ..................................................................................................................... 399 FACILITY TERMINATION S Introduction to Facility Terminations ....................................................................................... 401 Patch Panels ............................................................................................................................... 401 Patch Panel Connections ............................................................................................................ 404 Pigtail Dressing .......................................................................................................................... 407 | Fiberinstall.pdf |
Fiber-Optic Technology (680-10-7) Page 1 LESSON 1: Fiber-Optic Technology (680-10-7) Modules in this Lesson Fiber-Optic Technology Basics Light Sources Optical Receivers | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber Installation and Activation Page 2 MODULE 1 FIBER-OPTIC TECHNOLOGY BAS ICS Introduction to Fiber-Optic Technology Basics Since the first commercial installation of a fiber-optic network in 1975, fiber-optic technology has migrated and evolved from exclusive use in backbone applications to extending into the customer premises. From hybrid fiber/coax (HFC) to fiber-to-the-x (FTTx) architectures, fiber-optic technology is key to providing the physical media necessary for delivering the volume of information required by the end user today and in the future. Incorporating fiber-optic technology into the broadband cable system requ ires the fiber-optic cable technician to know the following: Fiber-optic technology fundamentals Optical light sources Optical receivers Advantages of Fiber Optics Describe the advantages of using fiber-optic technology. Fiber-optic technology was develo ped to overcome the associated costs and other transport issues of twisted-pair cable, coaxial cable, microwave, and satellite communications. There are many benefits to using fiber-optic technology to deliver broadband signals, including: Transmits video, voice, and data signals to meet all communications services. Increases the reliability of the distribution network. Decreases the cost of network maintenance. Provides the most cost-effective means to upgrade network bandwidth. Provides an economical yet technically superior method of consolidating multiple headends. Increases the physical reach of signals. | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber-Optic Technology (680-10-7) Page 3 Since optical fibers are typically made of glass, a dielectric material, they are virtually immune to electromagnetic interference (EMI), including radio frequency interference (RFI). Although not wholly immune from electromagnetic pulse (EMP) radiation, optical fibers resist EMP and its devastating effects. Therefore, though mostly exposed, the fiber-optic cable portion of the communications network is the least vulnerable element subject to interruption due to EMP radiation. In addition, fiber-optic cable is manufactured to operate at temperatures from-40°F to +160°F, and fiber-optic cable is affected less by moisture and thermal conditions than copper. The result is less signal degradation due to extreme weather conditions and mechanical failure. Because there is no EMI, RFI, or other detectable energy radiating from the cable, the signal transport through fiber-optic cable is very secure. Physically tapping in to an optical fiber creates a substantial network signal loss and immediately alerts network monitors. Data rates through optical fibers have been transmitted at more than 73 terabits per second (Tbps), capable of handling 5. 5 million simultaneous high-definition television (HDTV) video channels. Theoretical data rates are estimated to be up to 200-500 T bps. A single optical fiber, operating at 10 gigabits per second (Gbps), can handle over 9. 2 million equivalent voice channels (or thou sands of video channels). In addition, a 3/4-inch round fiber-optic cable can be manufactured with up to 864 optical fibers, which weigh approximately 130 pounds per kilometer. A twisted-pair cable containing a comparable number of conductors over the same distance weighs 16,000 pounds. This lighter weight allows for longer stretches of fiber-optic cable between splice points and easier installations. The glass dielectric used in most optical fiber is manufactured from silica, the material that comprises sa nd, which, unlike copper, is abundant worldwide. Since the optical fiber is made of dielectric material, the cable does not carry electrical current, radiate energy, or produce heat or sparks. As a result, the all-dielectric fiber-optic cable provides a sa fe transport medium for signals in dangerous or explosive environments. Signal loss through fiber-optic cable is significantly lower than other transport media, such as coaxial cable, twisted-pair cable, and microwave. As a result, signals can be transport ed over longer distances and with greater signal quality. Fewer repeaters or amplifiers are required due to lower signal attenuation, the increased performance of light sources and detectors, and continuous improvements in connectors and splicing techniques ( Figure 1 ). Figure 1 : Repeater used in fiber-optic network. (Courtesy of Light Brigade) | Fiberinstall.pdf |
Fiber-Optic Te chnology Basics Fiber Installation and Activation Page 4 Fiber-optic cable can meet changing network topologies and configurations, allowing for lower-cost operations growth and service expansions. Technologies like bi-directional transport, optical switching, and optical multiplexing are widely available to upgrade and reconfigure network designs. Industry Standards Organi zations Identify organizations that have set standards for fiber-optic technology. The fiber-optic industry has international and national video, voice, and data standards. In addition, test and measurement, installation, and design standards have continued to evolve to meet the users' requirements. New generations of standards by the International Telecommunication Union (ITU), Telecommunications Industry Association (TIA), International Electrotechnical Commission (IEC), Institute of Electrical and Electronics Engineers (IEEE), and Society of Cable Telecommunications Engineers (SCTE) continue to push the development and implementation of fiber-optic technology. Of particular note are the many standards of the ITU, which is the creator of the world's most recognized communications standards, known as "recommendations. " The ITU Telecommunication Standardization Sector (ITU-T) designation encompasses all video, voice, and data. ITU-T G-series recommendations address optical system design and engineering considerations. Table 1 lists some of the more common ITU-T G-series recommendations used in the broadband cable industry, along with a brief description. Characteris tics Series Description Optical Fiber G. 655 Non-zero-dispersion-shifted fiber (NZDSF) operating at 1550 nanometers (nm). G. 653 Zero dispersion, dispersion-shifted fiber (DSF) operating at 1550 nm. G. 652 Standard single-mode fiber (SMF) operating at 1310 nm. G. 652. D Single-mode fiber with reduced water peak; also called low water peak (LWP) and zero water peak (ZWP). G. 657. A Bend-insensitive fiber (BIF) used inside buildings; minimum bend radius of 10 millimeters (mm). G. 657. B BIF used inside buildings; minimum bend radius of 7. 5 mm. Optical Systems G. 694. 2 Defines wavelength and channel spacing for coarse wavelength division multiplexing (CWDM) at 1271 to 1611 nm. G. 692 Defines transport bands, components, and optical interfaces for dense wavelength division multiplexing (DWDM). | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber-Optic Technology (680-10-7) Page 5 Characteris tics Series Description G. 671 Transport characteristics of optical components and subsystems. Fiber-to-the-x (FTTx) Fiber-to-the-x (FTTx) Systems G. 983 BPON ( broadband passive optical network) ; general installation diagram. G. 984 GPON (gigabit passive optical network) ; general characteristics of FTTx systems. G. 987 XGPON (10-gigabit pas sive optical network). G. 986 Ethernet operating at 1 Gbps. Transmission Standards G. 709 OTN ( optical transport network). Table 1 : ITU-T G-series recommendations. Electromagnetic Spectrum and Wavelength Identify the common wavelengths used in fiber-optic communications. All electromagnetic waves travel at the speed of light, which (measured in a vacuum) is approximately 300,000,000 (300 × 106) meters per second (186,291 miles per second). For centuries, scientists have quantified the colors of light, or frequencies, by the distance between the top of one light wave and the top of the next; that is the reason for the name "wavelength" ( Figure 2 ). The lowercase lambda symbol (λ) represents wavelengths in many drawings and texts. The metric system, which works well w ith prefixes to express length and distance, is used to communicate and measure a wavelength. The wavelength is calculated by dividing the speed of light by the carrier wave frequency. For example, a 300-megahertz (MHz) carrier would have a wavelength of one meter (300 × 106 ÷ 300 × 106 = 1), and a 3,000 MHz carrier would have a wavelength of 0. 1 meter (300 × 106 ÷ 300 × 109 = 0. 1), or 100 millimeters (mm). The higher the carrier wave frequency, the shorter the wavelength. Figure 2 : One wavelength. | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber Installation and Activation Page 6 The electromagnetic spectrum, shown in Figure 3, encompasses energy from radio waves to Gamma rays. Optical wavelengths are measured in nanometers (nm) or billionths of a meter (10-9). Accordingly, in the visible light spectrum, violet light has a wavelength of approx imately 380 nm (7. 85 × 1015 hertz [Hz] ) or 7. 85 petahertz (PHz), and red light has a wavelength of approximately 700 nm (4. 3 × 1015 Hz or 4. 3 PHz). SMF transports wavelengths at 1310 nm (2. 29 PHz) and 1510 nm (1. 99 PHz), just below the visible light frequency spectrum. Figure 3 : Electro magnetic spectrum. In fiber-optic terminology, " window " refers to a center optical wavelength and a range of wavelengths on either side of the center wavelength. The water peak absorption area of the fiber has higher than usual attenuation. There are four standard optical windows ( Figure 4 ), each with a nominal wavelength : 850 nm, 1300 nm, 1550 nm, and 1625 nm. The 1300-nm window is used for multimode fiber (MMF) at 1300 nm and SMF at 1310 nm. Otherwise, the 850-nm window is used exclusively for MMF, while the 155 0-and 1625-nm windows are used exclusively for SMF. | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber-Optic Technology (680-10-7) Page 7 Figure 4 : Fiber-optic transport windows with d B/km vs. wavelength curves. (Courtesy of Light Brigade) Early fiber networks operated between 850 nm and 1300 nm using MMF. SMF became available in 1983 and had lo wer signal attenuation and greater information-carrying capacity. Three years later, single-mode optical networks began operating in the lower loss, 1550-nm window. In the mid-1990s, a new window operated in the 1625-nm range, primarily used for optical te sting of "out of band" information, such as alarm channels. To maintain the distinctiveness of an optical amplifier's spectral width, the ITU specified and designated bands based on exact single-mode fiber wavelengths instead of using the window terminology. The bands ( Table 2 ), similar to the frequency bands of radio, g roup the wavelength ranges in a defined and logical manner. For example, the conventional band, or C-band, between 1530 and 1565 nm, is specified around the amplification range of the erbium-doped fiber amplifier (EDFA). Type Band Wavelength Range (nm) Original O-band 1260 to 1360 Extended E-band 1360 to 1460 Short S-band 1460 to 1530 Conventional C-band 1530 to 1565 Long L-band 1565 to 1625 Ultra long U-band 1625 to 1675 Table 2 : ITU SMF transmission bands. | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber Installation and Activation Page 8 Basic Fiber-Optic Communications Networks List the three basic elements of a fiber-optic communications network. Figure 5 illustrates the three basic components of all fiber-optic communications networks: (1) Optical transmitter with a light so urce to convert electrons to photons (2) Optical fiber as a transport medium (3) Optical receiver with a photodetector to convert photons to electrons Figure 5 : Fiber-optic network basic components. (Courtesy of Light Brigade) When learning about fiber-optic communications networks, it is essential to understand how each one of these components operates together as a system. | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber-Optic Technology (680-10-7) Page 9 The optical transmitter in Figure 6 has an electrical interface providing one or a combination of electrical protocols to the data encoder/modulator. The encoder portion of the data encoder/modulator codes analog signals for conversion into digital signals, and the modulator portion transforms the digital signal into the appropriate modulation format. The modulation signal is app lied to the light source, which could be either a light-emitting diode (LED) or a laser diode. The intensity of the optical signal from the light source varies in proportion to the applied modulation signal, creating a modulated optical signal, which is then coupled to the optica l fiber for transport to the optical receiver. Figure 6 : Electrical signal to optical signal conversion. The optical signal travels through the fiber to an optical receiver containing a photodiode (or detector), which converts the modulated light signal to a modulated electrical signal. The received and amplified electrical signal is th en sent to a data decoder or demodulator. The demodulator then converts the transport signal to the original protocol and format (video, voice, and data). Optical Fiber Basics Describe the three basic parts of optical fiber. Optical fiber is used to trans port light signals from the laser transmitter to the receiver. An optical fiber is made up of three parts: Core —Transports the majority of the optical signal Cladding —Surrounds the core Protective coating —Covers the cladding | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber Installation and Activation Page 10 Figure 7 shows the differences in the diameter and physical structure of MMF and SMF. Figure 7 : MMF and SMF dimensions. (Courtesy of Light Brigade) MMF has a large core diameter with many optical layers, allowing light to take several pathways, or modes, from one end of the fiber to the other. High data rate information is then spread across the different modes and is difficult for the optical receiver to detec t. As a result, the information-carrying capacity of MMF is limited to relatively low data rates. The 9-micron (μm) core diameter of SMF is small compared to the overall fiber diameter. The small core size and uniformity of the glass manufactured in a step-index profile forces light to travel in a single pathway, down the fiber's axis, with the capability of carrying high data rates and large volumes of information. The cladding, which surrounds the core, has a lower refractive index than the core to keep most of the optical signal internally reflected within the core. However, due to the optical fiber's mode field diameter (MFD), up to 20% of the optical signal may be carried in the core's surrounding area, which is the cladding nearest the core ( Figure 8 ). Figure 8 : MFD. The ITU has developed standards defining the MFD for each type of optical fiber and wavelength (Table 3 ). | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber-Optic Technology (680-10-7) Page 11 ITU-T Specification Wavelength Mode Field Diameter G. 652 1310 nm 8. 6-9. 5 ± 0. 6 mm G. 653. A 1550 nm 7. 8 to 8. 5 mm ± 0. 8 mm G. 654 1550 nm 9. 5 to 10. 5 mm ± 0. 7 mm G. 655. C 1550 nm 8 to 11 mm ± 0. 7 mm G. 656 1550 nm 7 to 11 mm ± 0. 7 mm G. 657A 1310 nm 8. 6 to 9. 2 mm ± 0. 4 mm Table 3 : ITU standards. The coating applied during the final manufacturing process is outside the cladding. The coating is made from plastic materials and provides protection against bending, dam age to the glass surface, environmental effects, and mechanical stress. Splicing and connecting optical fibers require incredibly tight tolerances due to the critical need to align the centralized cores. Optical fibers used in outside plant applications h ave a standard diameter of 250 µm, which includes a 5 µm color coating for visual identification. The TIA/EIA-598-B standard for fiber color identification covers up to 24 fibers. However, there are typically only 12 fibers in a bundle, so those fibers and their color codes are most commonly used ( Figure 9 ). In bundles of 24 fibers, the color code repeats at fiber 13 with a black tracer added to fibers 13-19 and 21-24. Fiber 20 is black with a yellow tracer since a black tracer on a black fiber would be invisible. Figure 9 : TIA/EIA-598-B optical fiber color code. | Fiberinstall.pdf |
Fiber-Optic Technology Basics Fiber Installation and Activation Page 12 Fiber-optic cable has been developed for optimal performance at specific wavelengths. Today, two types of SMF are used extensively in fiber-optic networks: the ITU-T G. 652 fiber, commonly known as standard SMF, and the ITU-T G. 655 NZDSF. Standard SMF is optimized for operation in the 1310-nm band and can also transport 1550-nm optical signals. NZDSF is optimized for optical multiplex applications in the 1550-nm band and, though not optimal, can also transport 1310-nm optical signals. | Fiberinstall.pdf |
Fiber-Optic Technology (680-10-7) Page 13 MODULE 2 LIGHT SOURCES Introduction to Light Sources In any fiber-optic communications network, a laser diode, or light-emitting diode (LED), is the light source that generates the optical signal that is transported through the optical fiber. Light source selection can vary based on performance and application requirements. To carry information, the generated light, or optical carri er, is modulated using techniques that vary the intensity of the generated light. The fiber-optic cable technician should recognize the advantages and disadvantages of the different light sources in addition to the different types of optical modulation and demodulation. Light Source Selection Factors Describe the factors in selecting a light source for a fiber-optic network. Many products are available, so determining which light source will deliver the best performance for its application is crucial. All optical sources emit light over a range of wavelengths and have the following: Spectral width Emission pattern Coupled output power Peak wavelength Speed The term full width at half maximum (FWHM) is used to characterize a wavelength's spectral width or bandwidth. The spectral width is defined as the breadth of optical emission at intersect ing points of a line drawn across the emission's signature profile, 3 decibels (d B) (or 50%) of its power down from the original peak power amplitude. Figure 10 compares the spectral profiles of light-emitting diodes (LED) and laser optical sources. | Fiberinstall.pdf |
Light Sources Fiber Installation and Activation Page 14 Figure 10 : LED and laser light common spectral profiles. (Courtesy of Light Brigade) The emission pattern of the light source is directly related to the amount of light coupled to the core of an optical fiber ( Figure 11 ). Lasers have very narrow emission patterns that, when coupled to the small core of the single-mode fiber (SMF), allow enough optical power to be coupled to handle the long-distance transport of information. Standard LEDs emit light in all directions, so coupling light into a n optical fiber is relatively inefficient. However, some complex and expensive LEDs provide high output power levels and high-speed performance. Both light sources (laser and LED) emit most of their optical power around the center wavelength of the emissio n pattern. Figure 11 : Laser diodes coupled to small SMF core. When transporting digital information, the source's spectral width and data rate depend on rise time, the rate of how quickly the semiconductor in the device responds to on/off pulsing measured in nanoseconds (ns). For laser diodes with rise times less than 1 ns, the laser's ba ndwidth will be in the gigahertz (GHz), while an LED with a rise time of a few ns will exhibit bandwidths only in the megahertz (MHz). | Fiberinstall.pdf |
Light Sources Fiber-Optic Technology (680-10-7) Page 15 Laser Diodes Identify the types of lasers used for analog and digital communications networks. The laser, an acronym for "light amplification by stimula ted emission of radiation," was invented in 1960 by Ted Maiman of Hughes Research Laboratories ( Figure 12 ). However, the laser's development as a communications medium is directly attributed to Charles Kao, an electrical engineer and physicist who, in the 1960s, pioneered methods to combine glass fibers with lasers to transmit digital data. Laser diodes, also known as semiconductor lasers, are the light source most often used in high-performance fiber-optic communications networks. The laser diode provides the perfect union of a light source with SMF necessary for high-speed digital networks and noise-sensitiv e analog fiber networks. In addition, the laser diode's small spectral width, improved coupling efficiency, and fast modulation speeds are ideal for communications networks. Single-mode fiber-optic networks use Fabry-Perot (F-P) and distributed feedback (DFB) la sers. Figure 12 : Ted Maiman and the first laser. (Courtesy of Kathleen Maiman) Figure 13 depicts an optical spectrum analyzer display s howing wavelengths as side modes on either side of the center or peak wavelengths of the laser. These side m odes are caused by slight energy level differences between individual atoms, which create photons of slightly different wavelengths to be emitted and distinguished as a broadening of the laser's spectral width. Some of these photons could trigger their own stimulated emission processes, similar to several lasers of slightly different wavelengths operating simultaneously. | Fiberinstall.pdf |
Light Sources Fiber Installation and Activation Page 16 Figure 13 : Optical spectrum analyzer display of laser output. Fabry-Perot Lasers In the F-P laser illustrated in Figure 14, light-generating material is placed in an optical cavity between a set of highly reflective surfaces aligned perfectl y parallel to create a laser chip. An output light beam is available at both reflectors, but a partially reflective photodetector is placed at one end of the laser chip to monitor the beam power. The beam's power information is fed back as an electrical signal to the laser's drive circuitry to stabilize the output optical power level. At the reflective surface opposite t he reflective photodetector, the optical signal from the laser is available for connection to an optical fiber. | Fiberinstall.pdf |
Light Sources Fiber-Optic Technology (680-10-7) Page 17 Figure 14 : Semiconductor F-P laser cutaway view. (Courtesy of Jeff Hecht) In a laser, a drive current is applied to a light-generating lasing medium that causes photons to be spontaneo usly emitted. As the current increases, so do the emission of photons, resulting in light emission comparable to that of an LED ( Figure 15 ). At a specific current level, a single spontaneously emitted photon stimulates the emission of an identical photon from an excited atom. These two photons stimulate the emission of two more photons, and so on. It is at this current level, the laser threshold, where the laser action begins. Its output increases rapidly and linearly with an increase in the drive current. Figure 15 : LED and laser power/current levels. (Courtesy of Jeff Hecht) Because every generated photon is identical to the one that triggered the process, the laser beam consists of a limited range of wavelengths ( monochromatic ), with all light waves in phase ( coherent light). As a result, the laser output is highly directional with a narrow emission pattern. One of the | Fiberinstall.pdf |
Light Sources Fiber Installation and Activation Page 18 drawbacks of the F-P las er is the emission of several discrete wavelengths or side modes ( Figure 16 ). Since each wavelength travels through an optical f iber at slightly different velocities, signals using those wavelengths arrive at the receiving point at different times, a phenomenon called chromatic dispersion (CD). CD becomes a limiting factor when tran sporting high-speed data (HSD) over long distances since the receiver cannot detect the data in the signal. As a result, F-P lasers have speed and noise sensitivity limitations but are less expensive than other types of lasers. Because of their c omparatively low cost, F-P lasers were once considered ideal for use in the return path of broadband cable networks. However, the increased demand for return path bandwidth finds most broadband cable networks replacing F-P lasers with DFB lasers in the ret urn path. Figure 16 : F-P laser output. Distributed Feedback Lasers The DFB laser uses internal Bragg grating to allow only photons of one wavelength to reach the reflectors, thus suppressing the development of side modes ( Figure 17 ). The resulting high signal-to-noise ratio (SNR) and small spectral widths make DFB lasers ideal for analog, high-speed digital, and optical multiplexing networks. | Fiberinstall.pdf |
Light Sources Fiber-Optic Technol ogy (680-10-7) Page 19 Figure 17 : DFB laser optical spectrum characteristics. Most lasers are sensitive to temperature changes and power supply quality, both of which can cause the laser's output to change significantly —in intensity and wavelength —due to a minuscule change in temperature. Even small lasers ( Figure 18 A), p ackaged with drive electronics, can dissipate more than one watt of heat. DFB lasers are particularly sensitive to temperature variations and require greater thermal control, provided by additional circuitry ( Figure 18 B). | Fiberinstall.pdf |
Light Sources Fiber Installation and Activation Page 20 Figure 18 : Laser transmitter examples. (Courtesy of Light Brigade) Back reflections between the optical transmitter output and the fiber-optic connectors are of particular concern since any reflected optical energy can disrupt the laser's stimulated emission process and degrade the signal. Choosing transmitters and optical connectors with high optical return loss (ORL) minimizes the amount of reflectance. It is why, in most high-performance networks, using connectors with an angled physical contact (APC) polish is standard practice. | Fiberinstall.pdf |
Light Sources Fiber-Optic Technology (680-10-7) Page 21 Light-Emitting Diodes Identify the characteristics of light-emitting diodes used in fiber-optic networks. The LEDs used in fiber-optic networks are inexpensive optoelectronic devices that convert electrons to photons. Two common types of LED are edge-emitting and surface-emitting. Unlike the laser output, which contains a single primary w avelength, the output of an LED consists of a range of wavelengths with spectral widths up to 100 nanometers (nm). The LED light source can transmit data rates up to 622 megabits per second (Mbps) in hundreds of pathways, each carrying the same data coupled into a fiber in separate paths or modes —comparable to how light waves travel through multimode fiber (MMF). Because LEDs have such a broad spectral width, they are most effective when coupled to MMF, which has large-core diameters. Subsequently, LED use is mainly limited to MMF and, occasionally, as a light source for low-cost single-mode test equipment. Edge-emitting LEDs (Figure 19 ) are the more complex and expensive LED type since they have relatively narrow spectral widths, high output power le vels, and perform at high modulation rates. The full FWHM spectral width typically is about 7% of the central wavelength or approximately 92 nm at 1310 nm. The edge which emits light is tiny, typically 30-50 microns (μm), and provides efficient coupling to optical fibers that are similar in size. Figure 19 : Edge-emitting LED emission pattern. Compared to edge-emitting LEDs, surface-emitting LEDs ( Figure 20 ) have a simple structure, are inexpensive, offer low-to-moderate output power levels, and are capable of performing at low-to-moderate modulation rates. Surface-emitting LEDs emit light in all directions; therefore, even though the optical output power from the surface-emitting LED is as high or higher than the edge-emitting LED, most of the light is lost before coupling to an optical fiber. | Fiberinstall.pdf |
Light Sources Fiber Installation and Activation Page 22 Figure 20 : Surface-emitting LED emission pattern. Optical Modulation Describe how modulation is applied to an optical carrier. The light from an optical source contains no information until modulation is applied using either direct or indirect methods. Direct modulation is accomplished by turning the optical source on and off or by varying the light intensity proportionately to the modulation information. For example, using on-off keying (OOK), the modulation information is encoded into a digital signal so th at the light source is turned on to represent the "logical one" and turned off to represent the "logical zero" (Figure 21 A). For indirect modulation, also called external modulation, the light source is turned on and operates at a constant output level. When applying indirect modulation using OOK, an external shutter opens and closes, interrupting the light as the modulating signal changes logical states from one to zero ( Figure 21 B). | Fiberinstall.pdf |
Light Sources Fiber-Optic Technology (680-10-7) Page 23 Figure 21 : Optical modulation schemes. Direct Modulation Direct modulation works well with semiconductor light sources and is relatively simple and inexpensive since semiconductor light sources have a linear operating curve. When an analog electrical signal is applied to the drive current of the source, an insta ntaneous and proportional change in power from the laser, called intensity modulation, occurs. As long as the modulation signal remains on the linear portion of the source's operating curve, the resulting optical signal is relatively free of noise and distortion. The current changes that occur during direct modula tion cause a slight change in the instantaneous wavelength of the generated light from the optical source, called " chirp," a significant limitation of direct modulation. Many methods exist to offset and reduce chirp; however, complex driver and detector circuitry are required at high data rates. Indirect Modulation Networks with higher data rate speeds tend to u se indirect modulation at the expense of greater circuit complexity. Indirect modulation virtually eliminates chirp and provides isolation from back reflections for improved relative intensity noise (RIN) performance. In addition, since the optical power output is constant, the choice of optical source can be made independent of the source's ability to vary the light intensity in proportion to the electrical modulation signal. Indirect modulation can also be applied using an analog signal, with better perf ormance than direct modulation. | Fiberinstall.pdf |
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Fiber-Optic Technology (680-10-7) Page 25 MODULE 3 OPTICAL RECEIVERS Introduction to Optical Receivers In the fiber-optic network, the optical receiver detects and converts the optical signal into an electrical signal, then demodulates the modulated information from the electrical signal. Internal to the receiver is an optical detector, also known as a photodiode, which converts a flow of photons to a flow of electrical current —the opposite function of an optical light source. Two optical detector types are used in fiber-optic networks, the positive-intrinsic-negative (PIN) diode and the avalanche photodiode (APD). As with optical light sources, there are different types of optical receivers and performance parameters, which the fiber-optic network designer must consider to fulfill a network's requirements. Performance Criteria for Optical Receivers Describe the pe rformance parameters of an optical receiver. The optical source and optical receiver make up the beginning and end of the fiber-optic network. Therefore, the optical receiver should have performance and compatibility requirements similar to those of an opt ical transmitter. Optical receiver sensitivity specifies the minimum amount of optical power required to achieve specified receiver performance. Below the minimum power level, there is not enough light to trigger an electrical signal from the optical detec tor. Accordingly, efficient coupling to the optical fiber to transfer the maximum amount of optical power from the optical fiber to the receiver is a key operational parameter. However, knowing the receiver's specified maximum input power is just as import ant. The optical detector can be oversaturated with light if optical power levels exceed the detector's maximum rated level, resulting in nonlinear operation, causing distortion, data errors, and signal loss. | Fiberinstall.pdf |
Optical Receivers Fiber Installation and Activation Page 26 Several factors contribute to the optical recei ver's sensitivity, including noise, responsivity, response time, linear response, back reflection, and optical detector material. Noise degrade s the transported optical signal in a fiber-optic network and is the main factor in determining the sensitivity of an optical receiver. As shown in Figure 22, the optical input signal goes directly to the light detection/amplifier circuitry. Although present everywhere throughout the network, noise is most serious at the optical detector due to the weaker signal input levels. Since the optical signal from the fiber-optic cable and the resulting electrical current have low amplitude, the photodiode circuitry includes one or more amplification stages before the signal can be decoded/demodulated. Figure 22 : Optical receiver signal flow. Receiver noise can be classified into two types, thermal and shot noise. The ran dom motion of electrons in the optical detector and amplifiers causes thermal noise. Shot noise is caused by current fluctuations, which result during the conversion of photons to electrons. Additionally, dark current is a type of shot noise resulting from a current that continues to flow in the photodiode w hen there is no optical signal. Responsivity is the ratio of electrical power output as measured between the detector and the optical input, usually expressed in amperes (A) or volts (V) per watt (W ). It is directly related to sensitivity —the higher the responsivity of the photodetector diode, the better the optical receiver's sensitivity. The optical detector's responsivity varies with wav elength and the material used to manufacture the photodiode. The optical receiver's response time is based on the time required for a photodiode to respond to optical inputs and produce an external electrical circuit. The photodiode response time depends o n many variables, including rise time, fall time, photodiode capacitance, load capacitance, and photodiode design. | Fiberinstall.pdf |
Optical Receivers Fiber-Optic Technology (680-10-7) Page 27 Optical detectors operate as linear devices over a broad range of optical power. The graph in Figur e 23 shows the electrical output of an optical detector versus the input optical power. When the optical signal is below the optical detector's minimum input, there is only dark current ( a type of shot noise) at its output. When the minimum required input power threshold is achieved, the response line is curved, and there is an increase in thermal and shot noise. Saturation occurs when the maximum current that the detector can produce has been reached. After saturation, any additional power goes undetected, and the optical input is no longer detected "faithfully" as an electrical signal. After saturation, any additional power increase will not be detected. Since this is the case, the optica l input power to the optical detector must stay within the linear portion of the operational curve for low noise and faithful replication of the original optical signal. Figure 23 : Optical detector electrical output. Indium gallium arsenide (In Ga As) and other compounds are extensively used in fiber-optic receiver photodetectors. Figure 24 show s the spectral width of different materials used to make photodiodes. Silicon and gallium arsenide (Ga As) have narrow spectral widths, so they are unsuitable for 1310- and 1550-nanometer (nm) wavelengths. Germanium and indium gallium arse nide (In Ga As) have wider responses, which include 1310 and 1550 nm. However, germanium is noisy and suitable only for very low frequencies or for use in power meters. | Fiberinstall.pdf |
Optical Receivers Fiber Installation and Activation Page 28 Figure 24 : Typical spectral responses of various optical detector materials. (Courtesy of Jeff Hecht) PIN Diode Optical Detectors Identify the characteristics of the PIN diode optical detector. The positive-intrinsic-negative (PIN) diode is the most common photodiode used in optical receivers because it is relat ively inexpensive and can be operated from a standard power supply. The PIN diode, shown in Figure 25, has three semiconductor layers: (1) P-layer —Doped with a predominance of electron holes ("holes") (2) Intrinsic layer —Contains no charge and acts as an insu lator when the diode is reverse-biased, so there is no current flow (3) N-layer —Doped with a predominance of electrons When light photons strike the P-layer, the diode becomes forward-biased, causing the holes and electrons to travel and el ectrical current to flow through the intrinsic layer. The current flow is linear to the intensity of light photons, as one electron/hole pair is created for every absorbed photon until saturation. | Fiberinstall.pdf |
Optical Receivers Fiber-Optic Technology (680-10-7) Page 29 Figure 25 : Basic PIN diode structure. Avalanche Photodiode Optica l Detectors Explain the structure and attributes of an avalanche photodiode. The avalanche photodiode (APD) is a photomultiplier device with significantly increased sensitivity, approximately 10 decibels (d B) compared to the PIN diode, which can eliminate the need for a costl y repeater, thereby offsetting the increased cost of the APD. The uneven nature of the APD's multiplication process amplifies the electrical signal and also introduces noise into the electrical output. In addition, APDs require a higher voltage power supply and more complex circuitry than PIN diodes, which results in higher operating costs. Despite these costs, APDs are used in optical networks over long distances of fiber-optic cable or, in the ca se of fiber-to-the-x (FTTx) network architectures, where high attenuation levels caused by optical splitters must be overcome. | Fiberinstall.pdf |
Optical Receivers Fiber Installation and Activation Page 30 The APD functions like a simple PIN diode detector at lower voltages without amplification. Like PIN diodes, APDs create primary electr ical carriers from charged semiconductor materials sandwiched together to produce electronic flow when light photons strike ( Figure 26 ). However, if electric fields are high enough in the device, these primary carriers can accelerate and carry a lot of kinetic energy. If such a carrier strikes a neutral atom, the kinetic energy can bump a valence electron into the conduction band, creating another electron-hole pair called a secondary carrier. Depending on the field strength, th is collision ionization can generate tens or hundreds of secondary carrie rs, increasing external circuit currents by the same amount. This "avalanche" of secondary carriers is how the APD exhibits signal gain. Figure 26 : APD basic structure. APDs are biased to achieve a specified gain: the higher the bias, the higher the gain. However, if the bias voltage is too high, collision ionization will occur without incident photons, which decreases the device's signal-to-noise ratio (SNR). Bias voltages used to create the necessarily high electric fields must also be set at a high enough voltage, sometimes up to several hundred volts. Because gain is closely linked to bias, high-stability power supplies are required with APDs, making them more costly to use than PIN diodes. The rise time of an APD is extremely fast, but fall times may be a bit slower because extra time is required for the avalanche region to clear off secondary carriers formed by collisions. As a result, devices with higher gains have slower fall times. | Fiberinstall.pdf |
Optical Receivers Fiber-Optic Technology (680-10-7) Page 31 Detection and Demodulation Explain how optical detection and demodulation are used on an optical receiver. Most fiber-optic communications networks use a direct modulation scheme in which an electrical signal modifies the intensity of an optical carrier from within the optical transmitter. As shown in Figure 27, the optical carrier is transported through the fiber-optic network to an optical receiver. In the optical receiver, the optical detector converts the variable intensity of the optical carrier into an electrical signal that is representative of the modulating electrical signal. The optical detector performs two functions: converting an optical carrier to an electrical signal and demodulating the original modulated optical carrier. This “modulation, detection, demodulation” scheme is known as intensity modulation wi th direct detection (IM/DD). Figure 27 : IM/DD in an analog optical link. While IM/DD is reasonably simple and reliable, coherent detection techniques can improve the sensitivity of the optical receiver by as much as 20 d B. Moreover, coherent detection allows an optical signal's phase and polarization to be detected and, as a result, measured and processed. Subsequently, transport impairments through the optical fiber, such as chromatic dispersion (CD) and polarization-mode dispersion (PMD), can be mitigated electronically when the optical signal is converted into the electronic domain. Systems operating above 40 gigabits per second (Gbps) use coherent detection, allowing the greatest flexibility in advanced modulation formats. | Fiberinstall.pdf |
Optical Receivers Fiber Installation and Activation Page 32 As speeds of data tr ansmission increase, so does the occurrence of errors during transport. Forward error correction (FEC) data is added during the optical modulation process. The added FEC data allows the receiver to detect and correct errors within certain limits, which enables the receiver to operate with a lower receiv er-end optical SNR at the expense of a slightly lower data rate. Moving to higher data rates with advanced modulation techniques results in an optical signal-to-noise ratio (OSNR) deficit compared to 10G transmission over exis ting fiber links. FEC is a cost-effective solution to help close this deficit and, combined with coherent detection, allows optical transmission for terabit (Tb) transmission speeds. | Fiberinstall.pdf |
Fiber-Optic Cable Properties (680-20-6) Page 33 LESSON 2: Fiber-Optic Cable Properties (680-20-6) Modules in this Lesson Optical Fiber Types Fiber Performance Optical Fiber Dimension Tolerances | Fiberinstall.pdf |
Optical Fiber Types Fiber Installation and Activation Page 34 MODULE 1 OPTICAL FIBER TYPES Introduction to Optical Fiber Types The fiber optics industry has developed national and international standards for transmitting communications signals and protocols. In addition, the International Telecommunication Union (ITU), International Electrotechnical Commission (IEC), Telecommunications Industry Association (TIA), and the Society of Cable Telecomm unications Engineers (SCTE) introduced standards that continue to evolve. As worldwide fiber optics is projected to grow, these standards will continue to change to meet the user requirements and provide value for the optical fiber manufacturers and the cable operators that utilize optical fiber in cable networks. Fiber-Optic Basics Describe the components of a fiber-optic network. A fiber-optic network is a system that delivers reliable, high-speed, high-capacity communications. This system consists of th ree key elements: Laser transmitter —Emits optical power at a specific wavelength Optical fiber —The physical transport medium Optical receiver —Converts the optical signal back to an electrical format The optical fiber is also made up of three physical elements: Core —Transports most of the optical signal Cladding —Encapsulates the core Protective coating —Protects the glass during installation and handling Optical fiber diameters are measured in microme ters, commonly known as microns (μm), with the layer dimensions given from the inside out, core/cladding/coating, or core/cladding. For example, the diameters of the optical fiber in Figure 28 would be 9/125/250 or 9/125. | Fiberinstall.pdf |
Optical Fiber Types Fiber-Optic Cable Properties (680-20-6) Page 35 Figure 28 : Optical fiber with 9 µm core. (Courtesy of Light Brigade) There are two broad categories of optical fibers: single-mode fiber (SMF) and multimode fiber (MMF). The differences lie in their core diameters, physical structures, and optical profiles. SMF has a smaller core diameter than MMF, restricting the optical transport to one pathway or " single mode. " The advantage of single-mode transport is higher bandwidth capacity, faster transmission speed, lower attenuation, and lower fiber manufacturing costs than multimode optical fiber. As a result, SMF is used throughout the telecommunications industry. MMF, introduced in the 1970s, i s the oldest type of optical fiber used for optical communications. A large core (50 μm or 62. 5 μm) allows multiple modes, or paths, to be coupled from either laser or light emitting diode (LED) light sources operating at 850 nanometers (nm) or 1300 nm. As a result, less expensive optical sources and receivers are available for multimode operation, and multimode optical fiber continues to be used in many local area networks (LAN), securit y, and industrial applications. Single-Mode Fiber Describe the characteristics of standard single-mode fiber. The development of SMF in 1983 lowered attenuation levels to less than 0. 5 decibels per kilometer (d B/km) at 1310 nm and was later improved for use at both 1310 and 1550 nm. Today, the typical loss of single-mode fiber is 0. 4 d B/km at 1310 nm and 0. 25 d B/km at 1550 nm. For standard SMF, the dispersion has been optimized for use at 1310 nm, but this fiber can also be used for optical transport at 1550 nm with a lower att enuation level but with more signal dispersion. SMF is manufactured with a step-index profile, which means that the refractive index of the cladding is uniformly lower than that of the core. Only a single mode of light can be transported through the optical fiber when the wavelength of the light source is longer than a specific cutoff wavelength. At shorter wavelengths, the core has more room for higher-order modes to propagate, and the fiber operates as MMF. | Fiberinstall.pdf |
Optical Fiber Types Fiber Installation and Activation Page 36 SMF is available with two cladding types, matched-clad and depressed-clad. In the matched-clad optical fiber, the cladding has a constant refractive index up to the core boundary, resulting i n a step-index profile. In depressed-clad optical fiber, the inner cladding next to the core has a lower refractive index than the outer cladding. Matched-clad and depressed-clad fibers can be used interchangeably and can be spliced together. Because of it s larger mode field diameter (MFD), matched-clad fiber tends to be easier to splice, but it is slightly more sensitive to bend-induced attenuation. Optical fiber can be filled with certain chemical elements (a process called d oping) to provide refractive indexes tailored for specific applications. Therefore, the refractive index of fiber-optic cable varies between cable manufacturers and even the type of cable by the same manufacturer. Over the years, different optical fibers h ave been developed for optimal use at various wavelengths. Today, the International Telecommunicatio n Union (ITU) specifies ITU-T (ITU Telecommunica tions Standardization Sector) G. 652 and ITU-T G. 655 fibers, which are used extensively in fiber-optic networks and installations ( Table 4 ). ITU-T G. 652 fiber, commonly known as standard SMF, is optimized to transport 1310 nm wavelengths. ITU-T G. 655 is a non-zero dispersion-shifted fiber (NZDSF) intended to transport 155 0 nm and multiplexed wavelengths, such as dense wavelength division multiplexing (DWDM) applications. Attribute Detail G. 652 G. 655 Mode field diameter Wavelength 1310 nm 1550 nm Range of nominal values 8. 6-9. 5 µm 8-11 µm Tolerance ± 0. 7 µm ± 0. 7 µm Cladding diameter Nominal 125. 0 µm 125. 0 µm Tolerance ± 1 µm ± 1 µm Core concentricity error Maximum 0. 8 µm 0. 8 µm Cladding noncircularity Maximum 2. 0% 2. 0% Cable cutoff wavelength Maximum 1260 nm 1480 nm Chromatic dispersion coefficient Minimum zero-dispersion wavelength 1300 nm 1530 nm Maximum zero-dispersion wavelength 1324 nm 1565 nm Attenuation coefficient Maximum at 1310 nm 0. 40 d B/km Maximum at 1550 nm 0. 30 d B/km 0. 35 d B/km Maximum at 1625 nm 0. 40 d B/km 0. 4 d B/dm Polarization mode dispersion coefficient Maximum PMD Q 0. 5 ps/sqrt km 0. 5 ps/sqrt km Table 4 : ITU-T G. 652 and G. 655 SMF performance specifications. (Courtesy of Light Brigade) | Fiberinstall.pdf |
Optical Fiber Types Fiber-Optic Cable Properties (680-20-6) Page 37 Dispersion Shifting in Single-Mode Fiber Compare dispersion-shifted and non-zero-dispersion-shifted single-mode fiber. All SMF and MMF have optical attenuation and dispersion, which are related to specific wavelengths. Optical attenuation with zero dispersion in standard SMF is lowest at 1310 nm. The zero-dispersion point was shifted into the 1550 nm wavelength window to take advantage of SMF's low intrinsic absorption and lower attenuation at 1550 nm. The result was the development of dispersion-shifted fiber (DSF) and NZDSF. Dispersion-Shifted Single-Mode Fiber ITU-T G. 653 specifies DSF with zero dispe rsion at 1550 nm to exploit optical fiber's low intrinsic absorption at that wavelength ( Figure 29 ). Because of the optical fib er's low attenuation, DSF was used initially in oceanic installations and for attenuation-sensitive or long-haul terrestrial applications. Figure 29 : Zero-dispersion point shift from 1310 to 1550 nm. (Courtesy of Light Brigade) With zero dispersion at 1550 nm, as specified in ITU G. 653, light waves travel at the same velocity. When light waves are multiplexed and transported over long distances, the individual wavelengths interact with each other to create a distortion known as four-wave mixing (FWM), and new (undesired) wavelengths r esult. The new wavelengths mix together to produce sidebands at intervals dependent | Fiberinstall.pdf |
Optical Fiber Types Fiber Installation and Activation Page 38 upon the wavelengths of the interacting multiplexed light waves. As space between multiplexed light waves decreases, the FWM increases and is greatest near the zero-dispers ion point of the fiber. However, the presence of chromatic dispersion tends to neutralize FWM. DSF is no longer manufactured but remains used in many networks where optical multiplexing is limited or unused. Non-Zero Dispersion-Shifted Single-Mode Fiber NZDSF was developed to overcome the shortcomings of DSF when transporting multiplexed light waves. A small amount of dispersion introduced at 1550 nm forces the multiplexed wavelengths to travel at different velocities in the fiber, shifting above or below 1550 nm to prevent four-wave mixing ( Figure 30 ), reducing FWM and generating ne w (undesired) wavelengths. NZDSF was first manufactured in 1994 and is specified in the ITU-T G. 655 recommendation and TIA (Telecommunications Industry Associ ation) /EIA (Electronic Industries Alliance)-492E000 specification. NZDSF is optimized for operation at 1 550 nm, the optical fiber's lowest intrinsic absorption region. This optimization means that attenuation in SMF at 1550 nm is approximately 0. 25 d B/km, the lowest installed fiber attenuation to date. In addition, a new window at 1625 nm was opened as a mon itoring window for optical "out-of-band" information, such as network monitoring alarm channels. Figure 30 : Dispersion shifting to prevent four-wave mixing. (Courtesy of Light Brigade) Typical NZDSF dispersion values in the 1550 nm band are ±6 ps/nm/km (picosecon d per nanometer in one kilometer of fiber). These dispersion values are large enough to drastically reduce FWM while | Fiberinstall.pdf |
Optical Fiber Types Fiber-Optic Cable Properties (680-20-6) Page 39 retaining most of the benefit of DSF relative to SMF. When shifted below 1550 nm, the dispersion point is positive with respect to the zero-dispersion point. When shifted above 1550 nm, the dispersion point is negative with respect to the zero-dispersion point. The dispersion polarity is chosen to optimize the optical fiber for the specific application. Positive dispersion fiber is used in ne tworks where the optical fiber lengths are less than 1000 km. Negative dispersion fiber has extended reach and is used with digital laser sources in oceanic networks where the optical fiber lengths are well over 1000 km. Figure 31 shows the specifications for different types of NZDSF. | Fiberinstall.pdf |
Optical Fiber Types Fiber Installation and Activation Page 40 Figure 31 : Manufacturer NZDSF specifications. (Courtesy of Light Brigade) | Fiberinstall.pdf |
Optical Fiber Types Fiber-Optic Cable Properties (680-20-6) Page 41 Variations of Standard Single-Mode Fiber Describe some variations of the ITU-T G. 652 optical fiber specification. Additional applications for fiber-optic cable have dictated the need to modify the ITU-T G. 652 optical fiber specification. Coarse wavelength division multiplexing (CWDM) expanded the spectral bandwid th into an area identified as the water peak region, which is typically unusable for the transport of optical signals. The introduction of fiber-to-the-home (FTTH) architecture requires optical fi ber that is extra strong and resistant to damage and loss from bending due to improper installation. As a result, low water peak (LWP) SMF is specified in ITU-T G. 652. D, and bend-insensitive fiber (BIF) is specified as a variation to ITU-T G. 652 in recommendation ITU-T G. 657. Low Water Peak Single-Mode Fiber As shown in Figure 32, ITU-T G. 652 optical fiber has higher atte nuation in the spectral range between 1360 and 1460 nm, known as the E-band (extended band). This attenuation is caused by the absorption of hydroxide (OH) ions during the optical fiber manufactur ing process. As CWDM opened up the possibility of using the entire optical spectrum between 1260 nm and 1650 nm, fiber-optic cable manufacturers addressed the OH intrusion problem. The result was a new generation of ITU-T G. 652. D SMFs known as reduced wate r peak, LWP, or zero water peak (ZWP) fibers. These fibers have the same manufacturing tolerances as the older ITU-T G. 652 SMFs. They are also compatible with the older SMFs; however, they provide the capability of using CWDM in the E-band. Figure 32 : Optical fiber signal attenuation. (Courtesy of Light Brigade) | Fiberinstall.pdf |
Optical Fiber Types Fiber Installation and Activation Page 42 Bend-Insensitive Single-Mode Fiber With dense distribution and drop cable distribution populations installed into FTTH networks, space limitations to maintain proper bend radius became a challenge for optical fiber ins tallations. BIF is ideal for FTTH installations because the cable can handle smaller bend radius requirements. BIF is a variation of ITU-T G. 652 fiber and is designed to handle the smaller bend radius requirements of FTTH better than traditional ITU-T G. 65 2 fiber. Standardized by the ITU as "Bending Loss Insensitive Single-Mode Optical Fiber and Cable for the Access Network," the ITU-T G. 657 recommendation specifically calls out two fiber classes in ITU-T G. 657A and ITU-T G. 657B. With an operation range fro m 1260 nm to 1625 nm, ITU-T G. 657A optical fiber has LWP performance with a bend radius of 10 mm, compared to 30 mm for ITU-T G. 652. D fiber. ITU-T G. 657B has no water peak specifications, restrictive distances, nor specified dispersion but a bend radius of only 7. 5 mm. Figure 33 compares the bend radius of standard ITU-T G. 652 fiber to ITU-T G. 657 BIF. Figure 33 : Fiber bend radius compari son. (Courtesy of Light Brigade) Mismatching ITU-T G. 652 and G. 652. D fibers can cause attenuation increases up to 2 d B/km when operating in the E-band. Therefore, the type of fiber installed must be documented. | Fiberinstall.pdf |
Optical Fiber Types Fiber-Optic Cable Properties (680-20-6) Page 43 Multimode Fiber Explain how light is transported through multimode fiber. Modal dispersion, caused by signals traveling in different paths or modes through fiber and arriving at different times, occurs only in MMF. As a result, the input signal becomes blurred during transport, making it d ifficult to distinguish between data. As a result, the information-carrying capacity of MMF is limited. As signal transport distances and data rates increase, optical fiber with lower attenuation values and higher data rate capacity is required. Therefore, MMF is being replaced by SMF in many networks. Most MMF is manufactured with a graded-index profile, where the core's refractive index gradually decreases from the center of the core toward the cladding. The graded-index profile takes advantage of the refractive differences between eac h optical fiber layer to refract light back toward the core's center. Graded-index fiber is more costly to manufacture than the step-index fiber used in high-performance SMF. However, multimode transmitters and receivers cost less than single-mode devices. MMF can transport data rates from 10 to 100 megabits per second (Mbps) at distances ranging from 275 meters (900 feet) to 2 km (6,500 feet). Both the 50/125 and the 62. 5/125 MMF types ( Figure 34 ) are used extensively in private LANs, industrial controls, and closed-circuit TV (CCTV) security applications. Figure 34 : MMF with different core diameters. (Courtesy of Light Brigade) MMF types are specified in International Electrotechnical Commission (IEC) 11801 ( Table 5 ) and are categorized as OM1, 2, 3, and 4. Each has different bandwidths based on the core size and the type of light source used. | Fiberinstall.pdf |
Optical Fiber Types Fiber Installation and Activation Page 44 Designation Term Fiber (µm) Light Source OM1 Legacy 62. 5/125 LED OM2 Legacy 50/125 LED OM3 Laser-optimized 50/125 VCSEL OM4 Laser-optimized 50/125 VCSEL Table 5 : IEC MMF designations. (Courtesy of Light Brigade) | Fiberinstall.pdf |
Fiber-Optic Cable Properties (680-20-6) Page 45 MODULE 2 FIBER PERFORMANCE Introduction to Fiber Performance Because signal attenuation through optical fiber is considerably less than in other media such as twisted-pair, coaxial, and microwave transport, it is often the first choice for signal transportation over long distances. However, any unexpected or undesir ed attenuation, even as little as 1 decibel (d B), can have serious consequences. Five optical fiber properties determine how light is propagated: Optical attenuation Refractive index Total internal refraction Fresnel reflections Light dispersion Optical Attenuation Explain how signal attenuation occurs in fiber-optic cable. All transmission lines, including optical fiber, exhibit some loss or attenuation when transporting a signal. Much of the loss in fiber is intrinsic —the glass itself causes it. Howeve r, external conditions such as excessive bending can also contribute to signal loss. Table 6 shows the typical attenuation of single-mode fiber (SMF) in decibels per kilometer (d B/km) at 1310 nanometers (nm) and 1550 nm wavelengths. Wavelength Region Loss Distance 1310 nm 0. 35 d B 1 km 1550 nm 0. 25 d B 1 km Table 6 : Typical SMF loss per kilometer. Intrinsic Loss Intrinsic loss is typically caused by material absorption and Rayleigh scattering. Mate rial absorption is most common at 1385 nm and above 1700 nm due to residual metal ions and hydroxide (OH) ions, which | Fiberinstall.pdf |
Fiber Performance Fiber Installation and Activation Page 46 are introduced during the fiber's manufacturing process. Signal attenuation results when the light energy transported within the optical fiber is absorbed and converted to very small heat levels. The amount of material absorption varies with wavelength and depends upon the composition of the optical fiber. The International Telecommunication Union (ITU) specifies " low water peak (LWP) " fiber in ITU-T (ITU Telecommunications Standardization Sector) G. 652D fiber by stipulating that the attenuation at 1385 nm be as low as or lower than the optical fiber attenuation at 1310 nm. Rayleigh scattering is the reflection of light rays from molecular or optical impurities introduced during the fiber manufacturing process, accounting for 96% of all optical fiber attenuatio n (Figure 35 ). Light rays can scatter in all directions, but no signal attenuation occurs if the scattered light maintains an angle aligned with the forward signal within the core. Signal attenuation occurs when the light is scattered at an angle that is out of line with the signal's forward travel mode or path, and the light is diverted from the fiber core. Some scattered light i s reflected back toward the light source, which is what an optical time domain reflectometer (OTDR) measures to determine a fiber's length and to identify splices and anomalies in the fiber. Figure 35 : Light scattering in optical fiber. Because scattering increases as wavelengths get shorter, attenuation losses are higher at 1310 nm than at 1550 nm. In addition, wavelengths shorter than 800 nm are unusable due to excessive optical attenuation from Rayleig h scattering. Thus, attenuation through optical fiber is wavelength dependent due to material absorption and Rayleigh scattering. Macrobends and Microbends Macrobending and microbending losses are physical conditio ns that contribute to optical attenuation. Macrobending loss occurs when the fiber bend radius decreases. As the bend gets tighter, light rays within the fiber begin reflecting at angles that cause them to pass through the cladding and out of the fiber. Th e more the fiber is bent, the higher the attenuation ( Figure 36 A). Macrobending is typically found in splice trays and equipment chassis when the fiber bend radius decreases below the fiber manufacturer's minimum specification ( Figure 36 B). | Fiberinstall.pdf |
Fiber Performance Fiber-Optic Cable Properties (680-20-6) Page 47 Figure 36 : Macrobendi ng examples. (Courtesy of Light Brigade) Microbending can be intrinsic, beyond the technician's control, or extrinsic, within the technician's control ( Figure 37 A). Intrinsic microbending occurs as part of the fiber manufacturing process and is caused by minute deviations in the fiber core measured from the fiber's center. Extrinsic microbending losses arise from stresses on the fi ber caused by tight clamps, tie wraps, or rocks pressing against the fiber-optic cable ( Figure 37 B). Figure 37 : Microbending losses in SMF. (Courtesy of Light Brigade) Fiber tolerances and various fiber manufacturing methods can also create optical mismatches when | Fiberinstall.pdf |
Fiber Performance Fiber Installation and Activation Page 48 splicing optical fiber that can be categorized as both intrinsic and extrinsic loss. Table 7 lists causes of optical fiber attenuation categorized as intrinsic, extrinsic, or combinations of both. Intrinsic Loss Extrinsic Loss Intrinsic and Extrinsic Loss Absorption Connectors Couplers Fiber core mismatch Scattering Splices Macrobends Fiber numerical aperture mismatch Fiber core variations End finishes Microbends Different fiber manufacturing processes Microbends Attenuators Table 7 : Optical fiber attenuation. (Courtesy of Light Brigade) Refractive Index Explain the optical refractive index. When light passes through denser material, such as glass, it refracts or bends, causing its velocity to change. Accordingly, light traveling through a vacuum m oves faster than light traveling through denser materials. The refractive index, or index of refraction, measures how much the speed of light is changed when traveling through a material compared to traveling through a vacuum —the higher the refractive inde x, the denser the material. For example, the speed of light through a vacuum is 186,291 miles per second, and optical fiber has a refractive index of 1. 471. The speed of light through the fiber is 186,291 ÷ 1. 471, or 126,642 miles per second. Because glass can be infused, or doped, with certain chemical elements to provide refractive indexes tailored for specific applications, fiber-optic cables from different manufacturers wi ll have varying refractive indexes. Table 8 shows the refractive index for common single-mode optical fibers, listed by the ma nufacturer. Manufacturer 1310 nm 1550 nm Dispersion-Shifted and Non-Zero Dispersion-Shifted Corning: SMF-21 1. 468 1. 468 1. 476 Corning: SMF-28 1. 468 1. 468 N/A Corning: SMF-28E 1. 467 1. 468 N/A Corning: SMF-DS 1. 472 1. 471 N/A | Fiberinstall.pdf |
Fiber Performance Fiber-Optic Cable Properties (680-20-6) Page 49 Manufacturer 1310 nm 1550 nm Dispersion-Shifted and Non-Zero Dispersion-Shifted Corning: LEAF (NZDSF) N/A 1. 468 1. 469 Corning: LS (NZSDS) 1. 471 1. 470 1. 470 Corning: Metrocor (NZDSF) N/A 1. 469 N/A Draka 1. 464 1. 465 N/A Terawave (NZDSF) 1. 469 1. 469 1. 470 Furukawa 1. 452 1. 452 N/A OFS 1. 466 1. 467 N/A Truewave (NZDSF) 1. 471 1. 470 1. 470 Allwave (NZDSF) 1. 467 1. 468 1. 467 Sumitomo 1. 466 1. 467 N/A Table 8 : Common fiber-optic cable refractive indices. (Courtesy of Light Brigade) Total Internal Reflection Explain total internal reflection. In 1841, Daniel Colladon, a professor at the University of Geneva, demonstrated that light could be guided by focusing sunlight into a thin stream of water flowing through a hole in a water tank. When the light hit the water flow at a specific angle, he ob served that the light rays were trapped in the water stream. When light crosses between materials with different refractive indexes, such as air to water, if the angle of light is right, the light is absorbed by the water instead of reflected off the surfa ce. This phenomenon, called total internal reflection, is how light signals are "g uided," or transported, through the optical fiber. | Fiberinstall.pdf |
Fiber Performance Fiber Installation and Activation Page 50 When a light wave enters an optical fiber, the light wave refracts at an angle and travels slower. The direction of the refracted light depends on the angle of light entering the fiber, and as the angle changes, so does the refracted light's direction. At a certain critical angle, the light no longer passes between the two media but is reflected back as if the interface were a mirror. Total internal reflection also occurs in optical fiber since the fiber core is encapsulated by cladding with a lower refractiv e index (less dense). The difference in refractive indexes between the cladding and core causes light to be reflected off the cladding and back into the core along the fiber ( Figure 38 ). Even though the light undergoes many reflections when traveling along the fiber, no light is lost. Figure 38 : Light wave traveling through optical fiber core. Fresnel Reflections Describe Fresnel reflec tions and how they impact an optical network. Fresnel reflection is the change in the direction of a light beam at an interface between two dissimilar media so that the light beam returns to the medium from which it originated. As with a reflection in a mirror, the flatter the surface, the greater the reflection ( Figure 39 ). Fresnel reflection occurs at each fiber end, where the signal source enters or exits the cable, between media with different refractive indexes. A small signal loss can be expected at connector points due to signal reflections at the air-to-glass int erface. However, index-matching gels in connectors and mechanical splices can virtually eliminate Fresnel reflections. | Fiberinstall.pdf |
Fiber Performance Fiber-Optic Cable Properties (680-20-6) Page 51 Figure 39 : Optical connector Fresnel reflection. In digital networks transporting data at rates higher than one gigabit per second (Gbps), Fresnel reflections may create high bit error rates (BER). They might inte rfere with or compromise the stability of the laser in the transmitter. In analog networks, Fresnel reflections increase the noise received, which results in reduced signal-to-noise ratios (SNR). Fresnel reflection is one of the elements of optical return loss (ORL), which defines the t otal amount of reflectance in optical fiber. Light Dispersion Identify chromatic, polarization mode, and modal dispersion. When transported through an optical fiber, light waves tend to broaden over distance —a phenomenon called dispersion. Different types of dispersion appear in SMF and multimode fiber (MMF). Chromatic dispersion occurs at all wavelengths in SMF and MMF. At data rates of 40 Gbps and higher, polarization mode dispersion (PMD) also begins in SMF. Modal dispersion in MMF limits the use of this type of fiber for the transport of high-speed data (HSD). Chromatic Dispersion Chromatic dispersion in SMF is caused by the combination of material dispersion and waveguide dispersion in the optical fiber. Variations in the speed of light cause material dispersion through the optical fiber due to the optical material and the spectral width of the lig ht source. When data speeds become high enough, or the fiber is long enough, the pulses begin to overlap, resulting in errors. Each wavelength reflects off the cladding at a different angle when transported through the optical fiber. Due to the difference in the speed of light at each wavelength through the core, each wavelength arrives at | Fiberinstall.pdf |
Fiber Performance Fiber Installation and Activation Page 52 the other end of the fiber at a different time. Figure 40 illustrates an example of material dispersion as a narrow spectral transmission of three closely spaced wavelengths, which are spread apart when transported through an optical fiber. Material dispersion appears in MMF and standard ITU-T G. 6 52 SMF. Figure 40 : Optical fiber material dispersion. Waveguide dispersion only occurs in SMF because of its mode field diameter (MFD). As an optical signal travels through SMF, most of the signal is transported through the core. How ever, the fiber's MFD may allow up to 20% of the signal to be transported through the cladding. As illustrated in Figure 41, the refraction angle of the optical signal traveling through the fiber slightly changes when going from the core and into the cladding, then back into the core. This angle change occurs because the cladding is less dense (with a lower refractive index) than t he core. Thus, the optical signal travels faster through the cladding. The change in speed causes dispersion (represented as "w" in the illustration) in optical signals transported over long distances. As the refractive index varies for different wavelengt hs, the chromatic dispersion will also have different refractive index values. | Fiberinstall.pdf |
Fiber Performance Fiber-Optic Cable Properties (680-20-6) Page 53 Figure 41 : SMF waveguide dispersion. In material dispersion, the longer wavelengths travel faster than the shorter wavelengths, which is the opposite of what happens in waveguide dispersion. As a result, the two dispersions tend to counteract one another at different wavelengths. At approximately 1550 nm, the material dispersion completely cancels any waveguide dispersion, and zero dispersion occurs. The zero-dispersion wavelength of SMF can be moved by changing the refractive index profile of the optical fiber, which changes the waveguide dispersion. Polarization Mode Dispersion When operated above the fiber's cutoff wavele ngth, SMF carries two modes, magnetic and electrical, with different polarizations: horizontal and vertical ( Figure 42 ). In a p erfectly symmetrical fiber, the two modes travel at the same speed in a single mode but at different polarities. However, real-world fibers have slight differences in symmetry. When data rates reach 10 Gbps and higher, one of the modes begins to propagate slower than the other, and PMD begins to occur. As a result, the data pulses spread, and data errors occur. PMD effects at data rates of 100 Gbps are mitigated through coherent detection and forward error correction (FEC). | Fiberinstall.pdf |
Fiber Performance Fiber Installation and Activation Page 54 Figure 42 : Lightwave electric and magnetic field polarities. (Courtesy of Jeff Hecht) The degree of PMD in a fiber depends on factors such a s ambient temperature, bending, and stretching of the fiber. When a fiber is squeezed, bent, or stressed, the glass temporarily exhibits two refractive indexes, a phenomenon called birefringence, which also causes PMD. Therefore, PMD can occur randomly and fluctuate with environmental conditions, making it extremely hard to mitigate. An example of temporary PMD caused by environmental conditions occurs when a fiber-optic cable is installed beside a railroad track; the train vibration causes PMD to occur temporarily. New fiber-optic cable is being manufactured to minimize the amount o f PMD and its related effects. Modal Dispersion Modal dispersion, caused by different modes arriving at different times, limits the use of MMF. Because the optical fiber's glass is denser in the center than at the periphery, the modes of light traveling th e shortest distance down the middle of the core travel slower than the modes that take the longer paths along the outer part of the core. As optical pulses travel down an MMF, they begin to spread until they eventually spread into one another ( Figure 43 ). As the length of the fiber span increases, so does the data degradation from modal dispersion. | Fiberinstall.pdf |
Fiber Performance Fiber-Optic Cable Properties (680-20-6) Page 55 Figure 43 : Modal dispersion pulse spread ing. (Courtesy of Light Brigade) | Fiberinstall.pdf |
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Fiber-Optic Cable Properties (680-20-6) Page 57 MODULE 3 OPTICAL FIBER DIMENS ION TOLERANCES Introduction to Optical Fiber Dimension Tolerances Evolving manufacturing techniques have been instrumental in developing advanced optical networks using components such as optical filters, optical switches, ribbon fibers, and mass fusion splices. Unlike copper connections, optic al fibers require extremely tight tolerances due to the critical nature of aligning the central cores when splicing and connecting the fibers. The technician should know that the tighter the tolerances, the better the results when splicing optical fibers. The Core and Mode Field Diameter Describe characteristics of the mode field diameter in single-mode fiber. The core of single-mode fiber (SMF) has a step-index profile, meaning that the core's refractive index is uniformly higher than the surrounding cladding. Unlike multimode fiber (MMF), where all light is internally retained in the glass core, SMF transports some light in the surrounding cladding. Consequently, when defining the optical transport region of the fiber ( Figure 44 ), specifying the mode field diameter (MFD) is more accurate, technically correct, and critical to use than the core diameter. The larger the MFD, the easier it becomes to splice and connectorize —although the fiber becomes more sensitive to bending losses. | Fiberinstall.pdf |
Optical Fiber Dimension Toleranc es Fiber Installation and Activation Page 58 Figure 44 : SMF core and MFD tolerances. (Courtesy of Light Brigade) For most SMF, the power or light intensity follows a Gaussian or bell-shaped curve, with most light occupying the core ( Figure 45 A). The size of the mode field varies with wavelength, with longer wavelengths such as 1550 nanometers (nm) having a larger MFD than the same fiber at 1310 nm. While the MFD's physical size is larger than the actual core, approximately 80% of the light travels within the core, while the remaining 20% travels in the surrounding cladding. The MFD for standard SMF is specified by the International Telecommunication Union (ITU) in recommendation ITU-T (ITU Telecommunications Standardization Sector) G. 652 and G. 655 ( Figure 45 B), with MFD tolerances of ±0. 5 to ±0. 7 microns (µm). | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber-Optic Cable Properties (680-20-6) Page 59 Figure 45 : MFD elements and specifications. Core concentricity refers to how well the fiber core is centered within the cladding. Tolerances too loose yield poor quality splices and connections, especially when using fixed V-groove a lignment in fusion and mechanical splices. Figure 46 shows fixed V-groove alignment on a splicer where the only alignment is al ong the Z-axis as the fibers are brought together. The splice loss is determined by the precision of the V-grooves and the core/cladding concentricity of the fiber. The improved fiber tolerances of ±1 μm for SMF make it possible to achieve splice losses of only 0. 1 decibel (d B ). Since the V-groove establishes core alignment, the optical fiber's tolerance and the V-groove's cleanliness determine the splice's quality and accuracy. | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber Installation and Activation Page 60 Figure 46 : V-groove alignment. Cladding Dimensions Describe the cladding in single-mode fiber. Surrounding the core of the optical fiber is the cladding, usually made from pure silica glass. A lower refractive index than the core enables the cladding to keep most of the optical signal internally reflected within the fiber core. In SMF, the cladding's outside d iameter (OD) has been standardized as 125 µm, with an accuracy of ±1 µm ( Figure 47 ). SMF had cladding OD tolerances of ±2 µm as recently as 1990. | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber-Optic Cable Propertie s (680-20-6) Page 61 Figure 47 : SMF cladding. (Courtesy of Light Brigade) Dimension Tolerances When Splicing Describe splicing errors caused by variations in the optical fiber core and cladding dimensions. Over the years, improvements in manufacturing processes h ave resulted in optical fiber with very tight tolerances ( Table 9 ). Variations in the optical fiber core and cladding dimensio ns become most pronounced when optical fibers are spliced together. The splicing technician and splicing equipment have no control over fiber core and cladding dimensions, which, for SMF, have dimension tolerances of ±1 μm. Core/Cladding Tolerances Single-Mode Multimode Cladding diameter before 1968 ± 3 µm ± 3 µm Cladding diameter after 1988 ± 2 µm ± 2 µm Cladding diameter after 1993 ± 1 µm ± 1 µm Core diameter ± 1 µm ± 3 µm Mode field diameter ± 0. 5 µm N/A The core diameter can vary from one end of the fiber to the other. The optical characteristics vary from fiber manufacturer to fiber manufacturer. Table 9 : Common fiber-optic cable tolerances. (Courtesy of Light Brigade) | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber Installation and Activation Page 62 As a result, there are basically five splicing errors that can be attributed to differences between optical fibers: Core OD to core OD error MFD to MFD error Core OD to cladding offset error Cladding to cladding error Core concentricity error Core OD to c ore OD errors and MFD to MFD errors are difficult to distinguish from each other since diameter differences between spliced optical fibers cause both. A core OD of 8. 3 µm with a ±1 µm tolerance allows fibers from 7. 3 µm to 9. 3 µm to be within specification. In addition, an MFD of 9. 3 with a tolerance of ±0. 5 µm allows MFDs of 8. 8 µm to 9. 8 µm. Nothing the technician or the equipment can do will correct these error conditions, which are caused strictly by the diametric tolerances of the optical fiber. Fiber diameter differences between spliced fibers appear on an optical time domain reflectometer (OTDR) as gain splices in one direction ( Figure 48 A) and high-loss splices in the opposite direction (Figure 48 B). When taking an OTDR measurement, a gain splice or "gainer" occurs when a fiber with a larger MFD is spliced to one with a smaller MFD. It causes an increase in backscattered light, thus, a gainer. When measured from the other direction, the MFD at the splice goes from small to large. The change in backscatter typically appears as a splice with an excessive loss on the OTDR. Accordingly, many organizations, including the Telecommunications Industry Association in optical test procedure TIA-FOTP-61, recommend splice loss measurements in both directions. The value of the gainer and splice loss, which is always more than the gainer, is then averaged to determine the actual loss. | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber-Optic Cable Properties (680-20-6) Page 63 Figure 48 : OTDR traces show gainer and excessive splice loss. (Courtesy of Light Brigade) Core OD to cladding offse t errors, cladding to cladding errors, and core concentricity errors result from dimension differences between optical fibers that are still within specified tolerances. For example, if one fiber has a 124 µm cladding OD and the opposite has a 126 µm OD, t he initial core/MFD alignment will be off by 1 µm ( Figure 49 ). Fusion splicers with profile alignment system (PAS) and local injection and detection (LID) have motorized fixtures to align the mated fibers until the actual core and MFD are in the best possible alignment before the fibers are fused. These errors can be avoided by careful alignment when splicing individual fibers. Only the distance between the fibers can be adjusted when using a PAS, such as a V-groove, and these offset errors become more common. | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber Installation and Activation Page 64 Figure 49 : Core misalignment. (Courtesy of Light Brigade) Optical Fiber Coatings Describe the coating layer that is applied to optical fibers. Outside the cladding is the ultraviolet-cured acrylate coating applied over t he cladding during the final manufacturing process. The coating protects against bending and prevents damage to the glass surface from environmental effects and mechanical stress. Besides protection, the coatings must also: Function over a wide temperatur e range Be compatible with cable gels Adhere to the glass cladding over the lifetime of the cable Be mechanically strippable for splicing operations. In outside plant (OSP) applications, SMF is coated to have a standard 250 µm diameter with a ±5 µm toleran ce. A 5-µm colored layer is included in the coating to allow visual identification of each optical fiber, per the current TIA-598 standard ( Figure 50 ). Indoor-rated optical fiber and pigtails are coated to have a larger 900 µm diameter and can have tolerances of up to ±30 µm. Because plastic coatings have wider tolerances than the cladding, they were developed to be mechanically strippable so that the tight tolerances of the glass cladding can be used to align fibers for splicing accurately. | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber-Optic Cable Properties (680-20-6) Page 65 Figure 50 : TIA/EIA-598 optical fiber color coding. Ribbon Fibers Explain some of the benefits of ribbon optical fiber. The optical fibers can be grouped into ribbons of four to 36 fibers to save space in the fiber-optic cable, resulting in smaller diameter and higher fiber count cables. Ribbon cable can also be prepped and spliced much more rapidly than non-ribbon cable —this advantage lowers the per-splice and installatio n costs. Each ribbon is placed inside a colored buffer tube or organized by color-coded binders when used in a loose-tube fiber-optic cable. In Figure 51, six ribbons of 12 fibers are stacked in each binder to create a 6 × 12 ribbon stack. Th e ribbons are fabricated by sequentially layering the color-coded 250 µm fibers in a linear array. These arrays are then bonded together with a UV-cured plastic matrix material that can also be color-coded and labeled for quick identification. | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber Installation and Activation Page 66 Figure 51 : Ribbon cable cutaway. (Courtesy of Light Brigade) The specifications and concerns for the fibers used in ribbons are the same as loose-tube cables, except for fiber curl. Fiber curl describes the curvature that exists along a given length of fiber. While all fibe rs exhibit some curl, mass splicing of ribbon fibers requires that the fibers have good center-to-center spacings and lay flat in the fusion splicer's V-grooves. The lower the curl value, the better the attenuation uniformity of the individual splices. There are various types, counts, and manufacturers of ribbon cables and fiber. There are standard flat ribbons that not only come in 12-count but 24-and now 36-count. Essentially the 12-fiber flat ribbon is doubled or tripled side-by-side and held together w ith part of the same matrix that bonds the 12 single fibers that form the first flat ribbon together. It has a perforation that enables the flat ribbons to be separated from one another for splicing or "de-ribboning. " When these ribbons are stacked in a bu ffer tube or central tube in the OSP cable, counts of 864 fibers are not uncommon. Rollable and spider web ribbon (SWR) cables are capable of counts up to 10,368 fibers! More common are counts of 144 to 3,456 fibers. Cables containing ribbon fiber range in diameter from approximately one-half to almost 1. 5 inches for a cable containing 3,456 fibers ( Figure 52 ). | Fiberinstall.pdf |
Optical Fiber Dimension Tolerances Fiber-Optic Cable Properties (680-20-6) Page 67 Figure 52 : Sumitomo 3,456 fiber count, 250-µm thickness, color-coded optical fibers. (Courtesy of Sumitomo Electric Lightwave) Rollable-and SWR-type cables are only tacked at intermittent intervals to hold all the fibers together. However, handling and packaging of cables are easier due to the ribbon not having to maintain that flat structure; these cables can be rolled. When splicing, the ribbon is placed flat in a fiber holder, cleaved, loaded into the fusion splicer, and spliced. Most recently, fusion-splicers have been developed with 12-ribbon or 24-ribbon capacity at a time ( Figure 53 ). Part of being prepared is having the right splice case and correct splice trays to hold the larger diameter of a 12-or 24-count flat ribbon splice and slack. If the flat ribbon is 0. 5 inches wide, the tray must be much deeper than a standard splice tray depth. This deep tray is due to the flat ribbon structure having to route in the tray on its side. The splice holder will also need to accommodate ribbon heat shrink p rotectors that are wider and shorter than single-fiber protectors. Figure 53 : 12-count flat ribbon splicer. (Courtesy of Swift) | Fiberinstall.pdf |
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Introduction to Fiber-Optic Networks (680-15-6) Page 69 LESSON 3: Introduction to Fiber-Optic Networks (680-15-6) Modules in this Lesson Basic HFC Architecture Optical Nodes Fiber-Optic Network Services Fiber Transmission Standards Fiber Safety | Fiberinstall.pdf |
Basic HFC Architecture Fiber Installation and Activation Page 70 MODULE 1 BASIC HFC ARCHITECTU RE Introduction to Basic HFC Architecture Early cable televis ion (TV) networks were developed primarily to deliver local programming to communities where the reception of over-the-air (OTA) TV broadcast signals was poor. By the mid-1970s, satellite broadcast of video programming made it possible for broadband cable operators to offer additional channels to customers. Coaxial cable enabled engineers to design radio frequency (RF) transport networks effectively, and it remains an integral part of broadband cable architectures today. By using a combination of a fiber-optic transport backbone and a coaxial distribution plant, engineers developed hybrid fiber/coax (HFC) architectures. More recently, a new approach for offering video programming is done through Internet protocol television (IPTV) using video and audio compr ession technology, with fiber-to-the-x (FTTx) standards for fiber connectivity at the customer's location. The Headend Explain the various means by which signals are handled at a master headend. The headend facility performs several critical functions vital to maintaining a cable network's quality and technical performance. In addition to signal acquisition and transport functions, the headend is critical in element management and network monitoring. At the headend, local broadcast TV signals, satellite broadcast signals, and other content sources are received, processed, and assigned to radio frequency (RF) carriers and combined to create content channels for delivery to customers over hybrid fiber/coax (HFC) networks ( Figure 54 ). | Fiberinstall.pdf |
Basic HFC Architecture Introduction to Fiber-Optic Networks (680-15-6) Page 71 Figure 54 : HFC architecture. (Courtesy of Sorrento Networks) MPEG-2 (Moving Picture Experts Group) is the d ata transport method commercial TV broadcasters and satellite and cable TV operators use to deliver digital television (DTV). Multiple TV programs can be compressed and transported in a 6-megahertz (MHz) analog channel space using MPEG-2. MPEG standards have been universally accepted for DTV since the first MPEG standard ( MPEG-1) was released in 1992. MPEG has developed five standards for the digitally coded representation of moving pictures and associated audio storage, channel compression, decompression, transport, display, processing content description, and content prot ection ( Table 10 ). MPEG Standard Year Adopted Targeted Purpose MPEG-1 1992 Digital video and audio media storage at data rates up to 1. 5 megabits per second (Mbps). MPEG-2 1994 Display, transport, and storage of DTV. MPEG-4 1999 Interactive content, Advanced Video Coding ( AVC), and content distribution to the Internet and mobile devices. | Fiberinstall.pdf |
Basic HFC Architecture Fiber Installation and Activation Page 72 MPEG Standard Year Adopted Targeted Purpose MPEG-7 2001 Multimedia content description interface. MPEG-21 2003 Multimedia framework for metadata information for video and audio files and intellectual property management and protection. Table 10 : MPEG standards summary. Advanced Television Systems Committee (ATSC) defines the standards for DTV. The ATSC is not a Federal Communications Commission (FCC) committee but a consortium of cable operators, broadcasters, manufacturers, and governments whose mission is to standardize the technology for digital video. The ATSC uses the d igital encoding, transport, and multiplexing standards developed in MPEG-2. ATSC Standards: Channel bandwidth: 6 MHz per channel. MPEG-2: o Video compression standard o Transport, packetization, and multiplexing standard. 8-VSB or 16-VSB over-the-air (OTA) RF transmissions. DTV display formats: Aspect ratio Frame rates Types and lines of scanning Display resolution Since the 2009 FCC mandate to broadcast TV utilizing digital means, local bro adcasters began to transmit their signals in 8-VSB digital format. On June 12th, 2009, the last analog signal was turned off, marking the beginning of only digital broadcasting. VSB (vestigial sideband) modulation is the most efficient scheme for conserving bandwidth use because only one sideband is transmi tted fully while the second sideband is transmitted partially. Digital channel receivers receive and process 8-VSB signals. Equipment for routing Internet data and voice signals is also located in the headend. The combined carriers sent from the headend ca n be analog or digital quadrature amplitude modulation (QAM). Combined forward ( downstream ) broadcast signals, including voice and data carriers, are delivered to hubs and nodes using 1310 nanometers (nm) and 1550 nm optical transmitters that use traditional HFC transport architectures. The headend also provides the network elements needed to perform return path (upstream ) signal routing and processing. | Fiberinstall.pdf |
Basic HFC Architecture Introduction to Fiber-Optic Networks (680-15-6) Page 73 During the 1980s, fiber-optic technology was deployed throughout the cable TV indus try. Early fiber-optic applications included installing optical nodes to reduce the number of RF trunk amplifiers in cascade. Immediate benefits were realized from this configuration, such as outage reduction and improved picture quality. Fiber-optic links were also implemented to consolidate headends by linking them together. Baseband video signals could be digitally encoded and decoded using 1550-nm optical transport technology, allowing the signal originating in the master headend to feed a primary hub o r secondary headend facilities. Headends and Hubs Describe how a master headend transports signals to primary and secondary hub sites. Primary and secondary hubs are strategically placed throughout the serving area to distribute signals originating at the master headend. The master headend and headend/primary hubs are connected using primary ring fibers. Secondary fiber rings are used to connect the primary hubs with the secondary hubs. Fiber-optic ring topologies can provide high bandwidth and full redund ancy throughout the entire network. Data traffic, using ring topologies in conjunction with optical switching capabilities, can be rerouted from the opposite direction in the event of a fiber break or component failure ( Figure 55 ). Figure 55 : Regional ring network. | Fiberinstall.pdf |
Basic HFC Architecture Fiber Installation and Activation Page 74 Primary Hubs Primary hubs or headend/primary hubs are facilities that scale to serve large or small groups of customers depending on the customers and their requirements. Primary hubs perform many of the same functions as a master headend, but they differ from a headend in how they acquire signals. Primary hubs receive most data program content (video, phone, Internet) dire ctly from the master headend. The 1550-nm optical transport networks (OTN) were implemented in the 1990s to transport digitized video from a master headend to its primary hub sites ( Figure 56 ). Video signals originating from the master headend are converted to a digital bit stream and combined using time division multiplexing (TDM). Each TDM channel can contain up to 16 individual digital vid eo signals at a combined transmission rate of 2. 38 gigabits per second (Gbps). Figure 56 : Optical transport network. | Fiberinstall.pdf |
Basic HFC Architecture Introduction to Fiber-Optic Networks (680-15-6) Page 75 Eight wavelengths can be multiplexed onto a single fiber using dense wavelength division multiplexing (DWDM) for a total of 128 digitally encoded video channels transmitted over a single fiber, with a throughput of nearly 20 Gbps ( Figure 57 ). The ITU Telecommunications Standardization Sector (ITU-T) G. 655 standard defines characteristics of non-zero-dispersion-shifted (NZDS) fiber, which has been optimized for low attenuation and dispersion when operating in the 1550 nm window, making it suitable for DWDM applications. This type of fiber and wavelength are optimized for use with erbium-doped fiber amplifiers (EDFA) operating in the optical C-band (1530 to 1565 nm). Figure 57 : DWDM wavelength channels between 1530 and 1565 nm. The digital video signals are transmitted from the master headend to the primary hub locations over the primary optical transport rings ( Figure 58 ). At the primary hub locations, the DWDM wavelengths are demultiplexed and routed to digital receivers. The digi tal signals are converted back to the original video signals for modulation onto RF carriers. The RF carriers are combined to assemble a forward content lineup. Then, the forward broadcast channels can be delivered directly to the HFC plant using 1310-or 1550-nm AM optical transmitters. | Fiberinstall.pdf |
Basic HFC Architecture Fiber Installation and Activation Page 76 Figure 58 : DWDM transmission. While these synchronous optical network (SONET)-like digital video transport networks are still in use today, many cable operators are migrating to an MPEG-2 over Internet protocol (IP) /gigabit Ethernet (Gig E) solution to deliver video services on an IP backbone. MPEG-2 transport streams are optically delivered to hub sites using IP routers with optical SFP (small form-factor pluggable) transceiver interfaces. Some benefits of IP/Gig E include headend consolidati on and combining voice, video, and data services on the same IP backbone, reducing overhead and operational expenses. In addition, an IP backbone can use multiple optical transport standards such as wavelength division multiplexing (WDM), coarse wavelength division multiplexing (CWDM), or DWDM, which gives the provider sever al options to suit the needs of the business best. Forward channels being transported to secondary hubs can be accomplished using 1550 nm externally modulated lasers driving EDFAs capable of providing optical power levels over 20 decibel milliwatts (d Bm) (Figure 59 ). The output of the EDFA may be routed to an optical split ter array for distribution to multiple secondary hub sites. Primary hub facilities may also be used to house equipment for telephony and the routing of data and Internet traffic. | Fiberinstall.pdf |
Basic HFC Architecture Introduction to Fiber-Optic Networks (680-15-6) Page 77 Figure 59 : EFDA distribution to secondary hubs. Secondary Hubs Secondary hub sites are placed deeper into the serving area and provide service for smaller clusters of customers. The optical signals containing the forward broadcast lineup must be split at these locations to feed multiple optical receive rs (nodes). One or more EDFAs may be required to provide a sufficient power level before splitting the optical signal. Secondary hubs may contain equipment for the routing of data and Internet traffic. A single master headend can provide service to multipl e primary and secondary hubs using advanced ring topologies with additional deployment technologies used within HFC and FTTx network architectures. Virtual Hubs The virtual hub (V-Hub) can manage the complex functions of a hub site and allow operators to l aunch completely new system solutions like broadcast/narrowcast (BC/NC) amplification and combining radio frequency over glass (RFo G) and Ethernet passive optical network (EPON), all from a single hub ( Figure 60). | Fiberinstall.pdf |
Basic HFC Architecture Fiber Installation and Activation Page 78 Figure 60 : V-Hub The V-Hub looks just like a fiber node but can replace a traditional 20,000-customer hub facility even with its small size. The V-Hub helps the operator deploy advanced services quickly while also helping to control costs. It can be configured using plug-in modules to deliver residential services and is easily configured for more advanced services like those for commercial applications. Additionally, the V-Hub can: Be used to extend the reach of both the upstream and downstream distance limits. Deploy new services to leverage existing fiber infrastructures; EDFA's built into the module can amplify the light to overcome splitting and combining losses. Narrowcast, in some cases, around 24 unique downstream serving area feeds. Optical switches in the V-Hub can offer alternate routing and functions like those found in an OTN cabinet. Remote PHY Hubs Remote PHY (RPHY) is a distributed access architectu re (DAA) that moves the physical RF layer from the headend or hub to the edge of the access network ( Figure 61 ). It splits the headend components between the Media Access Control (MAC) Layer and the Physical (PHY) Layer, which means that the MAC functions like bandwidth scheduling and signaling can re main in the headend and the PHY functions can be pushed to another location at the network edge. | Fiberinstall.pdf |
Basic HFC Architecture Introduction to Fiber-Optic Networks (680-15-6) Page 79 Figure 61 : RPHY high-level architecture. The RPHY device (RPD) or DAA device at the network edge has circuitry like QAM modulators, upstream QAM demodulators, and com ponents that connect it to the Converged Cable Access Platform (CCAP) core. It can convert the downstream Data Over Cable Service Interface Specification (DOCSIS®), MPEG video, and out-of-band (OOB) CCAP core signals from Ethernet or passive optical network (PON) to analog for analog transmission over RF. For upstream DOCSIS and other sign als received in RF, the signal is converted to digital for transmission back over Ethernet or PON to the CCAP core. | Fiberinstall.pdf |
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Introduction to Fiber-Optic Networks (680-15-6) Page 81 MODULE 2 OPTICAL NODES Introduction to Optical Nodes Broadband cable service offerings continue to grow; the demand for increased network capacity has never been greater. As the need for more bandwidth challenges network providers to keep up with the pace of demand, many vendors are now producing new optical node designs, including scalable nodes, to meet the challenge. Optical Node Overview Explain the operation of optical nodes. In HFC architectures, the fiber-optic node is the i nterface between the optical transport and the coaxial plant ( Figure 62 ). Optical nodes provide both receive and transmit functi ons. The four main sections of the optical node are: (1) Otical receiver (2) Radio frequency (RF) amplifier module (3) Reverse optical transmitter (4) Direct current (DC) power supply | Fiberinstall.pdf |
Optical Nodes Fiber Installation and Activation Page 82 Figure 62 : Optical nodes. Optical signals that originate at the headend optical transmitter are converted to RF signals at the optical receiver located in the node. The RF signals are routed from the receiver output to an RF amplifier module and delivered to the coaxial plant through a diplex filter. Fiber-optic receivers can typically accept either 1310-nanometer (nm) or 1550-nm wavelengths. On the transmit side, upstream (reverse or return path) signals typically occupy the 5-42 megahertz (MHz) range. They are routed through a diplex filter to the input of the reverse optical transmitter. New amplifier designs for deplo ying Data Over Cable Service Interface Specification (DOCSIS) 4. 0 are extending the upstream spectrum to a new range of 5-65 MHz. These signals are modulated onto an optical carrier (OC) for transport back to the headend or hub location. Analog reverse optic al transmitters operate in the 1310 nm and 1550 nm ranges, while digital reverse optical transmitters may utilize dense wavelength division multiplexing (DWDM) wavelengths operating in the 1550 nm transmission window. Rev erse signal sources may include analog video carriers, cable modem data, voice services data, set-top box (STB) data, and status monitoring data. | Fiberinstall.pdf |
Optical Nodes Introduction to Fiber-Optic Networks (680-15-6) Page 83 Scalable Node Configuration Options Describe the different optical node configurations. One of the significant benefits of using a scalable node is that it offers a wide variety of configuration options, which allows for future network upgrades as needed. The varying complexity of the different configurations available, and the number of node receivers and transmitters, help accommodate ever-changing customer and network demands. Single Receiver and Transmitter Configuration The designation of node configuration options varies by manufacturer. In Figure 63, in which a node uses a single forward receiver and a single reverse transmitter, the standard node configuration is designated as 1 × 1 by Aurora Networks and Motorola, Inc. The first “1” denotes the number of forward optical receivers, and the second “1” i s the number of reverse optical transmitters. On the other hand, Cisco Systems, Inc. uses a separate designation for the forward and reverse paths. Cisco designates this standard node configuration as a forward 1 × 4, one forward receiver feeding four acti ve RF ports. They designate a reverse 4 × 1 ; four RF ports feeding one reverse optical transmitter. What actually occurs in this node is that one forward receiver provides the signal to four outputs using two separate RF modules. RF Module A routes signals to Ports 1 and 2, and RF Module B routes signals to Ports 3 and 4. All four ports are combined to feed a single reverse transmitter. Figure 63 : Single receiver and transmitter node configuration. Two Receivers and Two Transmitters Configuration Within the config uration in Figure 64, there are two separate forward receivers and two separate reverse transmitters. Aurora Networks and Motor ola designate this node as 2 × 2, with two forward receivers and two reverse transmitters. Cisco designates this node as a forward 2 × 4 configuration, with two forward receivers feeding four RF ports, and a reverse 4 × 2 configuration, with four RF ports | Fiberinstall.pdf |
Optical Nodes Fiber Installation and Activation Page 84 feeding two reverse optical transmitters. Receiver A provides signals to RF Module A, Ports 1 and 2, while Receiver B provides signals to RF Module B, Ports 3 and 4. Ports 1 and 2 are combined to feed reverse Transmitter A, and Ports 3 and 4 are combined to feed reverse Transmitter B. Figure 64 : Double receiver and transmitter node configuration. Four Receivers and Four Transmitters Configuration Figure 65 shows a fully loaded node that uses eight optical modules. It is designated as a 2 × 4 configuration with redundancy by Aurora Networks and Motorola. There are two active forward receivers and four reve rse transmitters. The other two forward receivers are used only in the event of a failure of the first two primary receivers. A local switch is provided to monitor the status of the receivers and control an RF relay. In the event of a failure at the primar y receiver, the local switch will route signals from the backup receiver to the RF module. Cisco designates this node as a forward 2 × 4 redundant configuration, with two active forward receivers feeding four RF ports, and a reverse 4 × 4 configuration, wi th four RF ports feeding four reverse optical transmitters. There is redundancy only in the forward path. | Fiberinstall.pdf |
Optical Nodes Introduction to Fiber-Optic Networks (680-15-6) Page 85 Figure 65 : Four forward receivers and four reverse transmitters node configuration. Status Monitoring Summarize the importance of using remote monitoring i n an optical node. Status monitoring is a technol ogy that allows the network operator to remotely monitor, pinpoint, and analyze malfunctions anywhere in the network. A status monitoring node transponder monitors many critical functions, including power supply voltages, transmitter/receiver status, and temperature, and it usually monitors a tamper switch mechanism as well. A status monitoring transponder receives downstream information from a controller located in the headend. It also generates an upstream telemetry carrier that is combined with the reverse optical transmitter input. This telemetry carrier allows the transponder to continuous ly communicate node functions with the controller located at the headend. Any parameters exceeding a preset threshold will generate an alarm. | Fiberinstall.pdf |
Optical Nodes Fiber Installation and Activation Page 86 Digital Return Path Transmission Explain the benefits of digital return path transmission systems. Broadband cabl e engineers can significantly reduce the costs of future network upgrades by using a digital transmission system in the reverse path. One advantage of a digital return system is increased link distances without performance loss. Also, the amount of fiber r equired in the network can be greatly reduced by using DWDM digital return transmitters in hub-to-headend architectures (Figure 66 ). Figure 66 : DWDM reduces network fiber requirements. A typical digital return transmitter has dual inputs. When the transmitter changes signals from analog to digital, each input is processed through an analog-to-digital (A/D) converter, producing a digital bit stream f rom the analog signal information. Then, the two data streams are combined through a multiple xer (MUX), creating one data stream, which drives the DWDM laser transmitter (Figure 67 ). | Fiberinstall.pdf |
Optical Nodes Introduction to Fiber-Optic Networks (680-15-6) Page 87 Figure 67 : MUX and DWDM laser within the return digital transmitter. At the receiving end of the link, the reverse processes take place. The optical data input is routed to a demultiplexer (DEMUX), which separates the two combined data streams ( Figure 68 ). Each data stream is passed through a digital-to-analog converter (D/A), which reproduces the original analog signal information present at the input of the digital transmitter. Because the input is digital, the dynamic range of the return path is greatly inc reased. Minimum optical input level requirements for a digital return receiver are in the-20-decibel milliwatt (d Bm) range, which allows for longer links without loss of performance. Figure 68 : Digital return receiver. | Fiberinstall.pdf |
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Introduction to Fiber-Optic Networks (680-15-6) Page 89 MODULE 3 FIBER-OPTIC NETWORK SERVIC ES Introduction to Fiber-Optic Network Services While the cable business began modestly by delivering a handful of television channels, the broadband business is now in an entirely different world, delivering hundreds of video channels, high-speed data (HSD), digital voice, sophisticated advert ising insertion, streaming video, and more. Today's optical fiber is widely used for various applications, realizing the benefits of greater bandwidth, faster speeds, longer distances, better reliability, more flexibility, and lower costs. Super headends u sed by large nationwide multiple system operators (MSO) are often placed in strategic high-altitude locations for optical reception of satellite signals. Fiber optic networks then carry these signals to smaller, more regional headends or primary hubs. Thes e super headends reduce costs by lessening the need for large headends in every smaller market. Video Signal Acquisition Describe methods for acquiring video signals at the master headend. Video signal acquisition primarily takes place at the master head end. Video signals can be acquired using several methods. Video programming is still obtained through broadcast satellites using C-band (3. 7-4. 2 gigahertz [GHz] ), Ku-band (11. 7-12. 2 GHz), and TV receive-only (TVRO) antennas, and direct-feed fiber-optic links. In June 2009, per the Digital Transition and Public Safety Act, TV broadcasters stopped analog transmission and began digitally transmitting all over-the-air (OTA) TV signals. Broadcast OTA digital television (DTV) signals are trans mitted using 8-VSB technology. | Fiberinstall.pdf |
Fiber-Optic Network Services Fiber Installation and Activation Page 90 By going all-digital, high-definition television (HDTV) became the new standard. The previous problems associated with the National Television Syste m Committee (NTSC) analog video signals, like ghosting, were eliminated overnight. Where analog broadcast was limited to only one program in a 6-megahertz (MHz) bandwidth, the transmission of an 8-VSB signal now allows multiple program transport streams to be assembled within a 6-MHz bandwidth. The net bit rate of 8-VSB is 19. 39 megabits per second (Mbps). MPEG-2 typically translates to one HDTV program or three standard-definition (SD) programs, depending on the program's content. With MPEG-4MPEG-4 AVC advanced video coding (AVC), two HDTV programs are possible. As a result of the transition to DTV, cable operators have upgraded headend equipment to accommodate the new digital signal format. 8-VSB digital receivers have replaced local analog signal processors that used to acquire the analog OTA broadcast signals. Carrying Voice Signals Describe how voice over Internet protocol is used in a cable system. Many cable operators have integrated technology within their networks to offer digital telephony services (DTS) to residential and business customers. Packet Cable TM has emerged as a means to provide DTS over hybrid fiber/coax (HFC) architectures. Voice over Internet protocol (Vo IP), also known as broadba nd Internet protocol (IP) telephony, is based on the Data Over Cable Service Interface Specification (DOCSIS) standard that is used for the delivery of high-speed data (HSD) service over an HFC network. Although early versions of DOCSIS, like DOCSIS 1. 0, were not intended to support voice services, DOCSIS 1. 1, 2. 0, 3. 0, and 3. 1 sta ndards were developed to overcome the latency and additional quality of service (Qo S) problems encountered with DOCSIS 1. 0 during its early IP telephony trials. These standards and specifications, called Packet Cable, were developed by Cable Labs® and its member companies to define the protocols required for IP telephony equipment. Operating in conjunction with the cable modem termination s ystem (CMTS) in the headend, additional equipment required for IP telephony includes a call management server, media gateway, signaling gateway, and a system to track records for billing purposes. A multimedia terminal adapter (MTA) is required to interface with end-user IP telephony equipment on the customer premises. The MTA is typically embedded into a DOCSIS modem, called an embedded multimedia terminal adapter (EMTA), used for HSD service ( Figure 69 ). | Fiberinstall.pdf |
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