Fiber Optics Jim Sluss University of Oklahoma Electrical & Computer Engineering [email protected] Outline • Part 1: Fiber Basics • Part 2: Fiber Optic Networks for Traffic and Transportation Systems • Part 3: Troubleshooting (Problems, Test & Measurement) Part 1: Fiber Basics Basic Communications Link Source Transmitter Channel Noise Receiver Interference Destination Basic Fiber Transmission Link Transmitter Drive Circuit Channel Light Source Receiver Photodetector Electrical Input Signal Amp Signal Restorer Electrical Output Signal Attenuation Distortion Electromagnetic Energy Rays of Light Photons Light is Oscillating Electromagnetic Energy Smallest Particle of light is called a Photon A Photon is a quantum or bundle of energy Only exists if the particle is in motion Electromagnetic Energy Magnetic Field Travels through free space @ 300,000 Km/sec or 186,000 Miles/sec In free space the Velocity of an Electromagnetic Wave is the Speed of Light 300,000 Km/sec Consists of Oscillating Electric and Magnetic Waves at right angles to each other Electric Field Electromagnetic Waves are Sinusoidal in shape Sine-Wave Positive Amplitude Negative Amplitude Wavelength Cycle Wavelength (Meters) = Frequency (Hertz’s) = The distance between the same points on consecutive waves The number of Cycles/sec Direction of Propagation Electromagnetic Energy Magnetic Field Travels through free space @ 300,000 Km/sec or 186,000 Miles/sec Wavelength = Velocity Wavelength = In free space the velocity of anMeters Electromagnetic Wave is the Frequency Velocityof Light = 300,000 300,000Km/Sec. Speed Km/sec Frequency = Hertz Consists of Oscillating Electric and Magnetic Waves at right angles to each other Question Electric Field What is the wavelength of 60 Hz ? Wavelength Sine-Wave Positive Amplitude Los Angeles Negative Amplitude = Electromagnetic Waves are Sinusoidal in shape 300,000 Km 60 Hz 5000 Km = 5000Km Boston 60 Hz Wavelength Cycle Wavelength (Meters) = Frequency (Hertz’s) = The distance between the same points on consecutive waves The number of Cycles/sec Direction of Propagation Electromagnetic Energy Magnetic Field Travels through free space @ 300,000 Km/sec or 186,000 Miles/sec Wavelength = Velocity Wavelength = In free space the velocity of anMeters Electromagnetic Wave is the Frequency Velocityof Light = 300,000 300,000Km/Sec. Speed Km/sec Frequency = Hertz Consists of Oscillating Electric and Magnetic Waves at right angles to each other Question Electric Field What is the wavelength of 2.4 GHz ? Electromagnetic Waves are Sinusoidal in shape Wavelength Sine-Wave Positive Amplitude = 300,000 Km 2.4 GHz = 125 microns Approximately the same diameter as a strand of human hair! Negative Amplitude Wavelength Cycle Wavelength (Meters) = Frequency (Hertz’s) = The distance between the same points on consecutive waves The number of Cycles/sec Direction of Propagation Electromagnetic Spectrum High Frequency Wavelength (nm) Ultra- Short Wavelengths Short 10 22 10 Cosmic Rays 21 Gamma Rays 10 20 10 19 10 16 10 Visible Light Sight Infrared Light 10 12 (1 THz) 10 11 10 10 10 9 (1 GHz) 10 Radar Television FM Radio Short-wave Radio AM Radio 8 10 7 10 6 (1 MHz) 10 5 10 3 10 2 10 0 455 Blue 490 Green 550 Yellow 580 Orange 620 Red 750 Infrared 800 Far Infrared 850 18K Hertz 10 4 (1 KHz) Violet Ultraviolet Rays 10 15 13 400 X-Rays 10 18 10 17 10 14 Ultra Violet Sound Sound Sub-sonic Low Frequency Long Wavelengths 20 Hertz Long Electromagnetic Spectrum Visible Light Ultra-Violet Violet Blue Green 400 455 490 550 Yellow Orange 580 Wavelength (nm) 1nm = Invisible Light 10 – 9 m 1m 1,000,000,000 620 Red Infrared 750 800 850 1300 1550 Fiber Optics Transmission The Speed Of Light Index of Refraction IOR The ratio of the speed of light in a vacuum to the speed of light in a specific medium Cladding Core 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 205,000 Km/s 225,000 Km/s 1.46 1.48 Fused Glass Fused Glass 1.33 300,000 Km/s 1 1.0003 Vacuum Air Water Material Velocity Journey of Light Angle of Incidence Ray Critical Angle Normal Glass I.O.R 1.48 Interface I.O.R 1.46 Refracted Ray Angle of Refraction Angle of = Angle of Incidence Reflection Advantages of Optical Fiber •Wide Bandwidth Flat •Low Loss OC192 129,024 Voice Channels 0.25dB/Km @ 1550nm •Electromagnetic Immunity •Light Weight •Small Size •Safety •Security Fiber is Dielectric, does not carry electricity Optical Fiber Two Types Of Fiber - Multimode & Singlemode Multimode • • Used for Low Bandwidth (less than 650MHz), Short Haul Communications with distances of up to 3Km (850nm) & 10Km (1300nm) Two operating wavelengths, 850nm and 1300nm Singlemode • Used for High Bandwidth, Long Haul Communications with distances of up to 40Km (1310nm) and 100Km (1550nm) or more • Two operating wavelengths at 1310nm and 1550nm Multimode Core / Cladding sizes 50/125, 62.5/125 and 100/140 microns Wavelength 850 & 1300nm Fiber Buffer 125 / 62.5 microns Cladding Core FDDI Fiber Distributed Data Interface Singlemode Wavelength 1310 & 1550nm Core less than 10 microns Cladding 125 microns Fiber Buffer 125 / 9/ 9/ 9microns Core Cladding Attenuation vs. λ Multimode Refractive Index Profiles • Multimode Stepped Index Fiber • Multimode Graded Index Fiber • Singlemode Stepped Index Fiber Multimode Stepped Index Fiber Cladding 140 microns Core 100 microns Input Refractive Index Profile Output Bandwidth Limited to about 150Mhz/Km Mode Time Scale Modal Multimode Graded Index Fiber Input Refractive Index Profile Output Bandwidth Limited to about 650Mhz/Km Mode Time Scale Modal Signal Distortion Important in determining the information capacity (bandwidth) of an optical fiber as a function of transmission distance. Intermodal Dispersion Intermodal dispersion - pulse spreading (in time) in multimode fibers, due to varying arrival times at the RX because each mode travels with a slightly different velocity. cladding mode 1 mode 2 core cladding Axial Cross-Sectio Singlemode Step Index Fiber Stepped Index, Terahertz Bandwidth Refractive Index Profile Wavelength / Attenuation / Distance 850nm Multimode 1300nm 1310nm 3.5dB/Km 4.28 Km 1.75dB/Km 8.75 Km 0.5dB/Km Singlemode 1550nm 0.25dB/Km 30 Km Dynamic Range =15dB Tx Rx P0 -15dBm LDL -30dBm BER 1x10 6 60 Km Wavelength / Attenuation / Bandwidth Multimode 850nm 1300nm 3.5dB/Km 100 MHz/Km 1.75dB/Km 650 MHz/Km Singlemode 1310nm 1550nm 0.5dB/Km Unlimited 0.25dB/Km Unlimited Four Four Operating Operating Wavelengths Wavelengths 850nm 1300nm 1310nm 1550nm Multimode Singlemode LED’s ELED’s LASER’s Fiber Cables Point-to-Point Digital Transmission Links • Link Requirements: – Transmission Distance – Data Rate or Bandwidth A designer has the choice of the following: 1) Fiber Multimode or single-mode Core size and refractive index profile Attenuation Numerical aperture 2) Source Laser diode or LED Emission Spectral width Output power Speed (bandwidth) Effective emitting area Emission pattern 3) Detector – Sensitivity (or responsivity) Speed (bandwidth) Operating λ Link Power Budget Analysis PS - PR ≥ [ αf L + m(lc) + n(lsp) + system margin ] where αf = fiber attenuation (dB/km) L = fiber length (km) m = number of connectors lc = loss per connector (dB) n = number of splices lsp = loss per splice (dB) PS = source output power (dBm) PR = receiver sensitivity (dBm) System Margin • System margin is typically specified at 6 to 8 dB to allow for new components, component aging, and temperature fluctuations. Link Rise Time Budget • One accepted method for determining the dispersion limitiation of a fiber optic transmission system is to calculate the system rise time, tsys, and ensure that it does not exceed 70% of the NRZ bit period. tsys = [ ( ttx)2 + ( tGVD)2 + ( tmod)2 + ( trx)2 ]1/2 Signal Coding where ttx = transmitter rise time (spec'd by manufacturer) tmat = material dispersion rise time = DσλL or tGVD = group-velocity dispersion ≈ |D|Lσλ where D = material dispersion σλ = source spectral width L = fiber length tmod = modal rise time 0 for single-mode fiber trx = receiver rise time (spec'd by manufacturer) Exercise A 1550 nm single-mode digital fiber optic link needs to operate at 622 Mb/s over 80 km without amplifiers. A single-mode InGaAsP laser launches an average optical power of 0 dBm into the fiber. The fiber has a loss of 0.25 dB/km, and there is a splice with a loss of 0.1 dB every km. The coupling loss at the receiver is 0.5 dB, and the receiver uses an InGaAs APD with a sensitivity of –39 dBm. a) Find the system margin. b) Find the system margin at 2.5 Gb/s with an APD sensitivity of –31 dBm. Solution PS - PR ≥ [ αf L + m(lc) + n(lsp) + system margin ] so we can calculate the system margin from system margin ≤ PS - PR - αf L - m(lc) - n(lsp) where PS = 0 dBm αf = 0.25 dB/km L = 80 km m=1 lc = 0.5 dB n = 79 lsp = 0.1 dB Solution (continued) a) PR = –39 dBm for a data rate of 622 Mb/s system margin ≤ 0 dBm – (-39 dBm) – (0.25 dB/km)(80 km) – (1)(0.5 dB) – (79)(0.1 dB) system margin ≤ 10.6 dB, which is very respectable b) PR = –31 dBm for a data rate of 2.5 Gb/s system margin ≤ 0 dBm – (-31 dBm) – (0.25 dB/km)(80 km) – (1)(0.5 dB) – (79)(0.1 dB) system margin ≤ 2.6 dB, which is really not good enough to ensure long-term, problem-free operation of the link Exercise You are assisting with the design of an OC-192 fiber optic transmission link. Given a 1550 nm laser diode with a rise time of 25 ps and a spectral width of 0.1 nm, and a receiver with a rise time of 25 ps: a) Determine the maximum dispersion-limited transmission distance through a fiber optimized for a 1310 nm source (assume a material dispersion of 15 ps/nm-km). b) Determine the maximum dispersion-limited transmission distance through a dispersion-shifted fiber optimized for a 1550 nm source (assume a material dispersion of 2 ps/nm-km). Solution tsys = (ttx ) + (tGVD ) + (tmod ) + (trx ) substituting for tGVD = D Lσ λ 2 2 2 2 1 2 2 2 2 2 tsys = (ttx ) + ( D Lσ λ ) + (tmod ) + (trx ) and solving for L (t ) − ( t ) − ( t ) − ( t ) mod tx rx sys L= D σλ 2 2 2 2 1 2 1 2 Solution (continued) From the problem statement, ttx = 25 ps tmod ≈ 0 trx = 25 ps σλ = 0.1 nm For an OC-192, the data rate is approximately 10 Gb/s, so the NRZ bit period is Tb= 1x10-10 s = 100 ps. Thus, tsys should not exceed 70% of Tb, so set tsys=70 ps. Solution (continued) a) transmission through a fiber optimized for a 1310 nm source with D = 15 ps / nm ⋅ km. ( 70 ps ) − ( 25 ps ) − ( 25 ps ) = (15 ps / nm ⋅ km )(0.1nm ) 2 Lmax 2 2 1 2 Lmax = 40.28km b) transmission through a dispersion-shifted fiber optimized for a 1550 nm source with D = 2 ps / nm - km. ( 70 ps ) − ( 25 ps ) − ( 25 ps ) = ( 2 ps / nm ⋅ km )(0.1nm ) 2 Lmax Lmax = 302.08km 2 2 1 2 End of Part 1 Fiber Optic Networks for Traffic and Transportation Systems Part 2 ITS Communication Interface Concept Signal System NTCIP-Compatible Field Interfaces & Protocols Freeway/ Metropolitan Urban Suburban Rural TMC Interfaces CMS HAR Common Communication Network Infrastructure Ramp Metering Mediums (Wire, Wireless, Fiber) Field Masters Bridges, Routers, Multiplexers, Cross-Connects Infrastructure Interfaces Advantages: Share Data TMC Backup Shared External Interfaces Reduced Comms Costs Video Control Sensors Environmental External Interfaces Other State Agencies Private Services National State County Agency Options • Install-Operate-Maintain • Lease • Public/Private Partnerships Network Requirements • Data - Signal systems, VMS, video PTZ, vehicle detectors, sensors, etc. • Voice - Craft interfaces, HAR, emergency call boxes. • Video - Incident monitoring, surveillance, video detection. Analog vs. Digital Video? The answer drives required network bandwidth. Multiplexing Combines Two or More Signals into a Composite Signal for Transmission Separates out the Input Signals from the Composite to form Corresponding Outputs Multiplexing De-Multiplexing VOICE VOICE DATA DATA PLC PLC LAN LAN VOICE VOICE M M M M UU UU XX XX DATA DATA PLC PLC LAN LAN Network Topologies Ring Star Linear Fault-Tolerant Ring Topologies Primary Data Path Secondary Data Path Fiber Cut Typical Fiber Network Application SONET NODE SONET NODE Modem Controller Modem Controller SONET NODE Modem RS-232 Controller SONET NODE Modem Connections TCC Sensors Modem Controller Modem Controller Sensors Modem Controller Sensors Modem Controller Sensors Modem Controller Modem Controller Interconnect Diagram Hybrid Fiber/Wireless Network SONET NODE Antenna Radio Controller Antenna SONET NODE SONET NODE RS-232 Radio SONET NODE Antenna Protocol Interface TCC Protocol Interface Radio Sensors Protocol Interface Controller Protocol Interface Controller Controller SONET Synchronous Optical Network SONET Level (optical) OC-1 OC-3 OC-12 OC-24 OC-36 OC-48 OC-192 SONET Level (electrical) STS-1 STS-3 STS-12 STS-24 STS-36 STS-48 STS-192 Line Rate (Mb/s) SDH Level 51.84 155.52 622.08 1,244.16 1,866.24 2,488.32 9,953.28 STM-0 STM-1 STM-4 STM-8 STM-12 STM-16 STM-64 OC - Optical Carrier STS - Synchronous Transport Signal STM - Synchronous Transport Module SONET Multiplexing OC - 3 OC - 12 OC - 1 OC - 3 OC - 12 OC - 1 OC - 3 OC - 12 OC - 1 OC - 3 OC - 12 OC - 1 OC - 1 OC - 48 OC - 48 OC - 1 OC - 192 OC - 1 OC - 1 OC - 1 OC - 1 OC - 1 OC - 1 OC - 48 OC - 48 SONET Networking OC-192 OC-192 OC-192 Super - Express Layer OC-192 OC-192 OC-192 Super Capacity (WDM) OC-48 High Capacity (WDM) OC-48 OC-48 OC-192 OC - 3 OC - 3 Low Capacity Super Capacity OC-192 Express Layer OC-12 OC - 3 OC - 3 Low Capacity OC - 3 OC - 3 OC-12 Low Capacity OC- 48 OC-12 High Capacity OC- 48 OC- 48 Access Layer Transmission Over SONET • PCM Digital Hierarchy • ATM Over SONET • Packet Over SONET (POS) or IP over SONET Wavelength Division Multiplexing (WDM) 1300 nm 1550 nm 1300 nm WDM WDM 1300 nm 1550 nm 1550 nm 1300 nm WDM WDM 1550 nm Dense WDM (DWDM) TX λ1 TX λ2 TX λN . . . W D M (mux) W D M (demux) λ1 RX λ2 RX λN RX . . . Optical Transport Network (OTN) G.709 • For data rates of 10 Gb/s and above, optical transmission lengths decrease ¾OTN uses Forward Error Correction (FEC) to increase optical link distance • Need to transport a wide range of services ¾OTN offers flexible payload management with minimum additional overhead Optical Transport Network (OTN) G.709 • Minimize O/E/O conversions ¾End-to-end transport of optical channels without O/E/O conversions • Ability to manage emerging DWDM networks ¾OTN offers management capabilities in the optical domain Optical Transport Network Backbone IP Router Virtual Photonic Core Transport Network SONET (no electrical terminations) Photonic Transport Router ATM SONET Backbone IP Router ATM Photonic Transport Node DWDM Link Photonic Transport Router End of Part 2 Part 3 Troubleshooting Problems Test & Measurement Problems Typical Problems Low Levels Patchcord Fiber Optic Cable Patchcord TX Dirty Connectors RX Avoid Tight Bending Radius’s Ferrule Must be Clean Connectors not seated properly Pinched Fibers Tight bending radius’s Bad Patchcords Low Transmit Levels Key/Keyway must be engaged in mating hardware Avoid Stress Points Tie wrap Cinched Tight, Must be Loose Problems Typical Problems High Levels Patchcord Fiber Optic Cable TX Patchcord A RX Attenuators High Transmit Levels (LASER) Fixed Attenuator 5db increments Not enough Loss in Fiber Plant Barrel Type Variable Attenuator Screw adjustable Attenuator 3 to 30db 3 to 30db Problems Typical Problems No Receive Level Patchcord Fiber Optic Cable Patchcord TX Dirty Connectors RX Avoid Tight Bending Radius’s Ferrule Must be Clean Connectors not seated properly Bad Patchcord (Open) No Transmit Output Wrong Fiber Key/Keyway must be engaged in mating hardware Avoid Stress Points Tie wrap Cinched Tight, Must be Loose Test & Measurement Optical Loss Measurements Reference Measurement Patchcord 850nm Light Source Bulkhead Connection Patchcord Received Level Relative Reference Measurement -15.0dBm Ref0.00dBm 850nm Power Meter Test & Measurement Optical Loss Measurements Attenuation Measurement ---Forward Direction Bulkhead Connection Bulkhead Connection Patchcord Patchcord Fiber under test 850nm Loss Fiber Loss -5.00dBm 850nm Light Source Power Meter Test & Measurement Optical Loss Measurements Attenuation Measurement ---Reverse Direction Bulkhead Connection Bulkhead Connection Patchcord Patchcord Fiber under test Fiber Loss Loss -4.80dBm 850nm 850nm Power Meter Light Source Test & Measurement Recording the Results Cable # Fiber AB Loss BA Loss Test & Measurement OTDR Measurements OTDR DEAD ZONES Near End or Attenuation DZ Splice DZ Connector DZ End of Cable Test & Measurement OTDR Measurements 2 1 3 Splice Loss 1 2 LSA Two Point dB Loss 3 Distance between Markers Km Distance between Markers Km Test & Measurement OTDR Measurements---Optical Return Loss Increases Bit Error Rates ---- Problems with Reflections Large Reflection Increases Noise in Analog Systems Dirty Connectors also cause Reflections Optical Return Loss Small Reflection Large Reflection Flat Finish -14.5db PC Finish - 45db Cleave Fiber -14.5db Test & Measurement Set up an Electronic Data Base Fiber Characterization • Record losses for all useable wavelengths • Bi- Directional Loss Measurements • OTDR traces for 850 / 1300nm Multimode and 1310 / 1550nm Singlemode • Bi- Directional traces for each fiber End of Part 3
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