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Fiber-Optic Communication Systems An Introduction

Fiber-Optic Communication Systems An Introduction. Xavier Fernando Ryerson Communications Lab http://www.ee.ryerson.ca/~fernando . Why Optical Communications?. Optical Fiber is the backbone of the modern communication networks The Optical Fiber Carries: Almost all long distance phone calls

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Fiber-Optic Communication Systems An Introduction

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  1. Fiber-Optic Communication Systems An Introduction Xavier Fernando Ryerson Communications Lab http://www.ee.ryerson.ca/~fernando

  2. Why Optical Communications? • Optical Fiber is the backbone of the modern communication networks • The Optical Fiber Carries: • Almost all long distance phone calls • Most Internet traffic (Dial-up, DSL or Cable) • Most Television channels (Cable or DSL) • Most LAN, WAN and much more • One fiber can carry up to 6.4 Tb/s (1012 b/s) or 100 million conversations simultaneously

  3. Multimedia over Fiber • Fiber carries various media • Voice(SONET/Telephony) - The largest traffic • Video (TV) over • Hybrid Fiber Coaxial (HFC) or • Fiber-Twisted Pair/Digital Subscriber Loops (DSL) • Data – Internet traffic ‘Triple Play’ Information revolution wouldn’t have happened without the Optical Fiber

  4. Why Optical Communications? Lowest Attenuation: 0.2 dB/km at 1.55 µm band resulting in 100s of km fiber links without repeaters Highest Bandwidth of any communication channel: Single Mode Fiber (SMF) offers the lowest dispersion highest bit rate  rich content (broadband) up to 100 Gb/s or more Enormous Capacity: Via WDM that also offer easy upgradability, The ‘Optical Layer’: Wavelength routing, switching and processing all optically, which adds another layer of flexibility

  5. Why OPTICOMfor you? • Optical communications is a huge area • Basic knowledge in optics is required in many other fields • Power Engineering • Fiber optics in smart grids, optical ground wire • Biomedical • Optical Coherent Tomography • Optical sensing • Civil engineering, smart structures • VLSI – Intra chip communications

  6. Global Market for Fiber Optic Sensors Source BCC Market Research

  7. Elements of a Fiber Optic Link

  8. Elements of a Fiber Optic Link

  9. Elements of OPTICOM System • The Fiber – that carries the light • Single Mode Fiber (only one EM mode exists), offers the highest bit rate, most widely used • Multi Mode Fiber (multiple EM modes exist), hence higher dispersion (due to multiple modes) cheaper than SMF, used in local area networks • Step Index Fiber – two distinct refractive indices • Graded Index Fiber – gradual change in refractive index

  10. Elements of OPTICOM System • Optical Transmitter converts the electrical information to optical format (E/O) • Light Emitting Diode (LED): cheap, robust and used with MMF in short range applications • Surface emitting and edge emitting LED • LASER Diode: high performance and more power, used with SMF in high speed links • Distributed Feedback (DFB) Laser – high performance single mode laser • Fabry-Perrot (FP) lasers – low performance multimode laser

  11. Elements of OPTICOM System • Optical Receiver convertsthe optical signal into appropriate electrical format (E/O) • PIN Photo Diode: Low performance, no internal gain, low cost, widely used • Avalanche Photo Diode (APD): High performance with internal (avalanche) gain • Repeater: receives weak light signal, cleans-up, amplifies and retransmits (O/E/O) • Optical Amplifier: Amplifies light in fiber without O/E/O

  12. Wavelength Division Multiplexing • Fiber has the capability to transmit hundreds of wavelengths • Coarse WDM (CWDM) has ~20 nm wavelength spacing • Dense WDM (DWDM) has up to 50 GHz spacing • Once the fiber is in place, additional wavelength can be launched by upgrading transceivers

  13. Optical Amplifier & EDFA • An optical amplifier amplifies the light signal without converting to electrical • Very useful is WDM systems • Erbium Doped Fiber Amplifier (EDFA) works in 1550 nm band Continuous Wave (Constant)

  14. Brief Intro on Telecom Networks

  15. Long Haul Network Basics of Communication Networks

  16. Brief History of Networks Copper Telecom Networks: • 4 kHz analog voice local loop (between customers and central office – access end) still in Bell Telephone lines & 56k modems • Digital interoffice trunks using DS-1 (Digital Signal Type 1) • A voice signal digitized at a sampling rate of 8 kHz  8 bits/samples is DS-0 (64 kb/s) • Carried on a single twisted copper-wire pair • Required repeaters every 2 km to compensate for attenuation

  17. Digital Transmission Hierarchy (DTH) 64-kb/s circuits are multiplexed into higher-bit-rate formats Called Telephony or T-Networks This is Copper network

  18. First Generation Fiber Optic Systems Purpose: • Eliminate repeaters in T-1 systems used in inter-office trunk lines Technology: • 0.8 µm GaAs semiconductor lasers • Multimode silica fibers Limitations: • Fiber attenuation • Intermodal dispersion Deployed since 1974

  19. Second Generation Systems Opportunity: • Development of low-attenuation fiber (removal of H2O and other impurities) • Eliminate repeaters in long-distance lines Technology: • 1.3 µm multi-mode semiconductor lasers • Single-mode, low-attenuation silica fibers • DS-3 signal: 28 multiplexed DS-1 signals carried at 44.736 Mb/s Limitation: • Fiber attenuation (repeater spacing ≈ 6 km) Deployed since 1978

  20. Third Generation Systems Opportunity: • Deregulation of long-distance market Technology: • 1.55 µm single-mode semiconductor lasers • Single-mode, low-attenuation silica fibers • OC-48 signal: 810 multiplexed 64-kb/s voice channels carried at 2.488 Gb/s Limitations: • Fiber attenuation (repeater spacing ≈ 40 km) • Fiber dispersion Deployed since 1982

  21. Fourth Generation Systems Opportunity: • Development of erbium-doped fiber amplifiers (EDFA) Technology (deployment began in 1994): • 1.55 µm single-mode, narrow-band semiconductor lasers • Single-mode, low-attenuation, dispersion-shifted silica fibers • Wavelength-division multiplexing of 2.5 Gb/s or 10 Gb/s signals Nonlinear effects limit the following system parameters: • Signal launch power • Propagation distance without regeneration/re-clocking • WDM channel separation • Maximum number of WDM channels per fiber Polarization-mode dispersion limits the following parameters: • Propagation distance without regeneration/re-clocking

  22. Evolution of Optical Networks

  23. History of Attenuation

  24. Three Windows based onWavelength

  25. Fiber Network Topologies Core - Combination of switching centers and transmission systems connecting switching centers. Access- that part of the network which connects subscribers to their immediate service providers LWPF : Low-Water-Peak Fiber, DCF : Dispersion Compensating Fiber, EML : Externally modulated (DFB) laser

  26. Synchronous Optical Networks • SONET is the TDM optical network standard for North America (called SDH in the rest of the world) • De-facto standard for fiber backhaul networks • OC-1 consists of 810 bytes over 125 us; OC-n consists of 810n bytes over 125 us • Linear multiplexing and de-multiplexing is possible with Add-Drop-Multiplexers

  27. SONET/SDH Bandwidths

  28. Last Mile Bottle Neck and Access Networks Infinite Bandwidth Backbone Optical Fiber Networks A few (Gb/s) Virtually infinite demand end user Few Mb/s The Last Mile ? ? Additionally, supporting different QoS

  29. Fiber in the Access End Passive Optical Networks (PON) – No active elements or O/E conversion Fibre-Coaxial (analog) or DSL (digital) fibre-copper systems Radio over fibre (Fibre-Wireless) Systems Currently Drives the Market

  30. PON Bit-Rates & Timeline

  31. Hybrid/Fiber Coax (HFC) Cable TV Networks This is a sub carrier multiplexed analog access network

  32. Digital Subscriber Loop (DSL) Fiber Link • Digital fiber-copper (fiber-twisted pair) link • Multimedia (video, voice and data) • At least 3.7 Mb/s streaming is needed for quality video • Bit rate heavily depend on the length of the twisted pair link • New techniques like very high rate DSL (VDSL) • Many buildings in GTA have access to video over DSL

  33. Radio over Fiber (ROF) • RF signals are transmitted over fiber to provide broadband wireless access • An emerging very hot area • Many advantages • Special areas • Underground • Olympics London • Niagara Tunnel

  34. ROF for Fiber-Wireless Networks Central Base Station RAP RAP RAP Y Radio over Fiber (ROF) (Simple) Up/Down links Y 802.11 voice Y Single ROF link can support voice and data simultaneously Micro Cell

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