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Fibre-Optic Communication Systems

Fibre-Optic Communication Systems. History of Fiber Optics. John Tyndall demonstrated in 1870 that Light can be bent. Total Internal Reflection (TIR) is the basic idea of fiber optic. Why Optical Communications?. Optical Fiber is the backbone of the modern communication networks

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Fibre-Optic Communication Systems

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  1. Fibre-Optic Communication Systems

  2. History of Fiber Optics John Tyndall demonstrated in 1870 that Light can be bent Total Internal Reflection (TIR) is the basic idea of fiber optic

  3. 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) • One fiber can carry up to 6.4 Tb/s (1012 b/s) or 100 million conversations simultaneously • Information revolution wouldn’t have happened without the Optical Fiber ‘Triple Play’

  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, video sensors • Optical sensing • Structural monitoring • VLSI – Intra chip communications

  6. Fiber in Smart Grid

  7. Intra Chip Optical Links

  8. Biomedical Optical Sensing Example An optical fiber sensor for the continuous monitoring of carbon-dioxide partial pressure in the stomach.4 The sensor is based on the color change of a CO2-sensitive indicator layer

  9. Source BCC Market Research Fiber Optic Sensors

  10. Elements of a Fiber Optic Link

  11. 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

  12. 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

  13. 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

  14. 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

  15. Multiplexing Is the set of technique that allow the simultaneous transmission of multiple signals across a single data link.

  16. Multiplexing Types of multiplexing Digital Analog TDM diagram FDM WDM

  17. Wavelength division mutliplexing • a multiplexing technique working in the wavelength domain • An analog multiplexing technique to combine optical signal.

  18. History • The concept was first published in 1970, and by 1978 WDM systems were being realized in the laboratory. The first WDM systems only combined two signals. Modern systems can handle up to 160 signals and can thus expand a basic 10 Gbit/s fiber system to a theoretical total capacity of over 1.6 Tbit/s over a single fiber pair.

  19. WDM • In fiber-optic communications Wavelength –division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different (colours) of laser light to carry different signals.

  20. Most WDM systems operate on single mode fiber optical cables, which have a core diameter of 9 µm. Certain forms of WDM can also be used in multi-mode fiber cables (also known as premises cables) which have core diameters of 50 or 62.5 µm.

  21. Why Is WDM Used? With the exponential growth in communications, caused mainly by the wide acceptance of the Internet, many carriers are finding that their estimates of fiber needs have been highly underestimated. Although most cables included many spare fibers when installed, this growth has used many of them and new capacity is needed.

  22. Three methods exist for expanding capacity 1)installing more cables, 2) increasing system bit rate to multiplex more signals 3) wavelength division multiplexing.

  23. Type of WDM 1)CWDM 2)DWDM

  24. Dense Wavelength Division Multiplexing • DWDM • No official or standard definition • Implies more channels more closely spaced that WDM • DWDM-based networks create a lower cost way to quickly respond to customers' bandwidth demands and protocol changes. • A key advantage to DWDM is that it's protocol- and bit-rate independent.

  25. Coarse wavelength division multiplexing • CWDM • No official or standard definition • number of channals is fewer than in dense wavelength division multiplexing (DWDM) but more than in standard wavelength division multiplexing (WDM). • Laser emmission

  26. CWDM&DWDM • CWDM system have channel at wavelengths spaced 20 nanometers (nm). • DWDM 0.4 nm spacing • Energy • tolerance

  27. Benefits of WDM • WDM technology allows multiple connections over one fiber thus reducing fiber plant requirement. • This is mainly beneficial for long-haul applications. • Campus applications require a cost benefit analysis. • WDM technology can also provide fiber redundancy. • WDM provides a managed fiber service.

  28. 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

  29. 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

  30. 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

  31. 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

  32. Evolution of Optical Networks

  33. History of Attenuation

  34. 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

  35. 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

  36. SONET/SDH Bandwidths

  37. 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

  38. 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

  39. PON Bit-Rates & Timeline

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

  41. 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

  42. 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

  43. 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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