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DWDM Presentation

Basic Knowledge

edwardfahmi
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DWDM Presentation

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  1. DWDM(Dense Wavelength Division Multiplexing)Edward Fahmi 2013

  2. Outline • Introduction • Components • Forward Error Correction • DWDM Design • Summary

  3. Increasing Network Capacity Options Same bit rate, more fibers Slow Time to Market Expensive Engineering Limited Rights of Way Duct Exhaust More Fibers (SDM) Same fiber & bit rate, more ls Fiber Compatibility Fiber Capacity Release Fast Time to Market Lower Cost of Ownership Utilizes existing TDM Equipment WDM Faster Electronics (TDM) Higher bit rate, same fiber Electronics more expensive

  4. Types of WDM • Coarse WDM (CWDM) Uses 3000GHz (20 nm) spacing. Up to 18 channels. Distance of 50 km on a single mode fiber. • Dense WDM (DWDM) Uses 200, 100, 50, or 25 GHz spacing. Up to 128 or more channels. Distance of several thousand kilometres with amplification and regeneration.

  5. DWDM History • Early WDM (late 80s) Two widely separated wavelengths (1310, 1550nm) • “Second generation” WDM (early 90s) Two to eight channels in 1550 nm window 400+ GHz spacing • DWDM systems (mid 90s) 16 to 40 channels in 1550 nm window 100 to 200 GHz spacing • Next generation DWDM systems More than 80/160 channels in 1550 nm window 50 and 25 GHz spacing

  6. Why DWDM—The Business Case Conventional TDM Transmission—10 Gbps 40km 40km 40km 40km 40km 40km 40km 40km 40km TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR DWDM Transmission—10 Gbps OC-48 OC-48 OC-48 OC-48 120 km 120 km OC-48 120 km OC-48 OC-48 OC-48 OA OA OA OA 4 Fibers Pairs 32 Regenerators 1 Fiber Pair 4 Optical Amplifiers

  7. Drivers of WDM Economics • Fiber underground/undersea Existing fiber • Conduit rights-of-way Lease or purchase • Digging Time-consuming, labor intensive, license $15,000 to $90,000 per Km • 3R regenerators Space, power, OPS Re-shape, re-time and re-amplify • Simpler network management Delayering, less complexity, less elements

  8. Characteristics of a WDM NetworkWavelength Characteristics • Transparency Can carry multiple protocols on same fiber Monitoring can be aware of multiple protocols • Wavelength spacing 50GHz, 100GHz, 200GHz Defines how many and which wavelengths can be used • Wavelength capacity Example: 1.25Gb/s, 2.5Gb/s, 10Gb/s, 40Gb/s, 100Gb/s, 400Gb/s 0 50 100 150 200 250 300 350 400

  9. Optical Transmission Bands

  10. ITU Wavelength Grid l 1553.86 nm 1530.33 nm 0.80 nm  193.0 THz 195.9 THz 100 GHz • ITU-T l grid is based on 191.7 THz + 100 GHz • It is a standard for laser in DWDM systems

  11. L-Band:1565–1625nm 1600 800 900 1000 1100 1200 1300 1400 1500 C-Band:1530–1565nm Fiber Attenuation Characteristics Attenuation vs. Wavelength S-Band:1460–1530nm 2.0 dB/Km Fibre Attenuation Curve 0.5 dB/Km 0.2 dB/Km Wavelength in Nanometers (nm)

  12. Characteristics of a WDM NetworkSub-wavelength Multiplexing or MuxPonding Ability to put multiple services onto a single wavelength

  13. Outline • Introduction • Components • Forward Error Correction • DWDM Design

  14. Optical Add/Drop Multiplexer (OADM) DWDM Components l1 l1...n 850/1310 15xx l2 l3 Transponder (Transmitter-responder) Optical Multiplexer l1 l1 l1...n l2 l2 l3 l3 Optical De-multiplexer

  15. l2 OEO OEO OEO ln Transponders • Converts broadband optical signals to a specific wavelength via optical to electrical to optical conversion (O-E-O) • Used when Optical LTE (Line Termination Equipment) does not have tight tolerance ITU optics • Performs 2R or 3R regeneration function • Receive Transponders perform reverse function l1 From Optical OLTE To DWDM Mux Low Cost IR/SR Optics Wavelengths Converted

  16. More DWDM Components Optical Amplifier (EDFA) Optical Attenuator Variable Optical Attenuator (VOA) Dispersion Compensator (DCM / DCU)

  17. Typical DWDM Network Architecture DWDM SYSTEM DWDM SYSTEM DE-MUX DE-MUX TRP TRP VOA EDFA DCM DCM EDFA VOA MUX MUX Service Mux (Muxponder) Service Mux (Muxponder)

  18. Spectrally broad Unstable center/peak wavelength lc Power Power lc l l Partially transmitting Mirror Mirror Amplified light Active medium Laser Characteristics Non DWDM Laser Fabry Perot DWDM Laser Distributed Feedback (DFB) • Dominant single laser line • Tighter wavelength control

  19. Optical Amplifier Pout = GPin Pin G • EDFA amplifiers • Separate amplifiers for C-band and L-band • Source of optical noise • Simple • Co-directional (pumping) and Counter-directional

  20. OA Gain and Fiber Loss Typical Fiber Loss 25 THz 4 THz • OA gain is centered in 1550 window • OA bandwidth is less than fiber bandwidth OA Gain

  21. Erbium Doped Fiber Amplifier (EDFA) Isolator Coupler Coupler Isolator Erbium-Doped Fiber (10–50m) Pump Laser Pump Laser “Simple” device consisting of four parts: • Erbium-doped fiber • An optical pump (to invert the population). • A coupler • An isolator to cut off backpropagating noise

  22. Loss Management: LimitationsErbium Doped Fiber Amplifier Each EDFA at the Output Cuts at Least in a Half (3dB) the OSNR Received at the Input Noise Figure > 3 dB Typically between 4 and 6 • Each amplifier adds noise, thus the optical SNR decreases gradually along the chain; we can only have a finite number of amplifiers and spans and eventually electrical regeneration will be necessary • Gain flatness is another key parameter mainly for long amplifier chains

  23. Optical Multiplexing Filter • Thin-film filters. • Bragg gratings. • Arrayed waveguide gratings (AWGs). • Periodic filters, frequency slicers, interleavers.

  24. Thin-film Filter • The thin-film filter (TFF) is a device used in some optical networks to multiplex and demultiplex optical signals. • Use many ultra-thin layers of dielectric material coating deposited on a glass or polymer substrate. • This substrate can be made to let only photons of a specific wavelength pass through, while all others are reflected. • By integrating a number of these components, several wavelengths can be demultiplexed.

  25. Bragg Gratings • A Bragg Grating is made of a small section of fiber that has been modified by exposure to ultraviolet radiation to create periodic changes in the refractive index of the fiber. • Light travelling through the Bragg Grating is refracted and then reflected back slightly, usually occurring at one particular wavelength. • The reflected wavelength, known as the Bragg resonance wavelength, depends on the amount of refractive index change that has been applied to the Bragg grating fiber and this also depends on how distantly spaced these changes to refraction are.

  26. Arrayed Waveguides • In the transmit direction, the AWG mixes individual wavelengths, also called lambdas (λ) from different lines etched into the AWG substrate (the base material that supports the waveguides) into one etched line called the output waveguide, thereby acting as a multiplexer. • In the opposite direction, the AWG can demultiplex the composite λs onto individual etched lines. • Usually one AWG is for transmit and a second one is for receive.

  27. Periodic Filters, Frequency Slicers, Interleavers • Periodic filters, frequency slicers, and interleavers are devices that can share the same functions and are usually used together. • Stage 1 is a kind of periodic filter, an AWG. • Stage 2 is representative of a frequency slicer on its input, in this instance, another AWG; and an interleaver function on the output, provided by six Bragg gratings. • Six λs are received at the input to the AWG, which then breaks the signal down into odd λ and even λ. • The odd λs and even λs go to their respective stage 2 frequency slicers and then are delivered by the interleaver in the form of six discrete interference-free optical channels for end customer use.

  28. Outline • Introduction • Components • Forward Error Correction • DWDM Design • Summary

  29. Error Correction • Error correcting codes both detect errors and correct them • Forward Error Correction (FEC) is a system adds additional information to the data stream corrects eventual errors that are caused by the transmission system. • Low BER achievable on noisy medium

  30. Bit Error Rate 1 BER without FEC -10 10 Coding Gain BER floor -20 10 BER with FEC Received Optical power (dBm) -30 10 -46 -44 -42 -40 -38 -36 -34 -32 FEC Performance, Theoretical FEC gain  6.3 dB @ 10-15 BER

  31. FEC in DWDM Systems 9.58 G 10.66 G 9.58 G 10.66 G • FEC implemented on transponders (TX, RX, 3R) • No change on the rest of the system IP IP FEC FEC SDH SDH FEC FEC . . . . ATM ATM FEC FEC 2.66 G 2.48 G 2.48 G 2.66 G

  32. Outline • Introduction • Components • Forward Error Correction • DWDM Design • Summary

  33. DWDM Design Topics • DWDM Challenges • Unidirectional vs. Bidirectional • Protection • Capacity • Distance

  34. Attenuation: Reduces power level with distance Dispersion and nonlinear effects: Erodes clarity with distance and speed Transmission Effects • Noise and Jitter: • Leading to a blurred image

  35. Solution for Attenuation OpticalAmplification Loss OA

  36. Solution For Chromatic Dispersion Saw Tooth Compensation Dispersion Dispersion DCU DCU Fiber spool Fiber spool Total dispersion averages to ~ zero -D +D Length

  37. Fiber l 1 l 2 l 3 l 4 Fiber l 5 l 6 l 5 l 7 l 1 l 8 l 6 l 2 l 7 l 3 l 8 l 4 l 1 l 2 l 3 l 4 Fiber l 5 l 6 l 7 l 8 Bi -directional Uni -directional Uni Versus Bi-directional DWDM DWDM systems can be implemented in two different ways • Uni-directional: • wavelengths for one direction travel within one fiber • two fibers needed for • full-duplex system • Bi-directional: • a group of wavelengths for each direction • single fiber operation for full-duplex system

  38. Uni Versus Bi-directional DWDM (cont.) • Uni-directional 32 channels system 32 ch full duplex • Bi-directional 32 channels system 16 ch full duplex

  39. Unprotected Client Protected Splitter Protected Y-Cable and Line Card Protected DWDM Protection Review

  40. Unprotected 1 Client Interface 1 Transponder • 1 client & 1 trunk laser (one transponder) needed, only 1 path available • No protection in case of fiber cut, transponder failure, client failure, etc..

  41. Client Protected Mode 2 Client interfaces 2 Transponders • 2 client & 2 trunk lasers (two transponders) needed, two optically unprotected paths • Protection via higher layer protocol

  42. Optical Splitter Protection Working lambda Optical Splitter Switch protected lambda • Only 1 client & 1 trunk laser (single transponder) needed • Protects against Fiber Breaks

  43. Line Card / Y- Cable Protection working lambda Only oneTX active 2 Transponders “Y” cable protected lambda • 1 client & 2 trunk lasers (two transponders) needed • Increased cost & availability

  44. Designing for Capacity Distance Solution Space Bit Rate Wavelengths • Goal is to maximize transmission capacity and system reach Figure of merit is Gbps • Km Long-haul systems push the envelope Metro systems are considerably simpler

  45. Designing for Distance L = Fiber Loss in a Span Pin Pout Pnoise S G = Gain of Amplifier Amplifier Spacing D = Link Distance • Link distance (D) is limited by the minimum acceptable electrical SNR at the receiver • Dispersion, Jitter, or optical SNR can be limit • Amplifier spacing (S) is set by span loss (L) • Closer spacing maximizes link distance (D) • Economics dictates maximum hut spacing

  46. Link Distance vs. OA Spacing Amp Spacing 20 60 km 10 80 km Wavelength Capacity (Gb/s) 100 km 5 120 km 140 km 2.5 0 2000 4000 6000 8000 Total System Length (km) • System cost and and link distance both depend strongly on OA spacing

  47. OEO Regeneration in DWDM Networks • OA noise and fiber dispersion limit total distance before regeneration Optical-Electrical-Optical conversion Full 3R functionality: Reamplify, Reshape, Retime • Longer spans can be supported using back to back systems Long Haul

  48. 3R with Optical Multiplexer and OADM Back-to-back DWDM 1 1 • Express channels must be regenerated • Two complete DWDM terminals needed 2 2 3 3 4 4 N N 7 7 Optical add/drop multiplexer • Provides drop-and- continue functionality • Express channels only amplified, not regenerated • Reduces size, powerand cost 1 1 2 2 OADM 3 3 4 4 N N 7 7

  49. Outline • Introduction • Components • Forward Error Correction • DWDM Design • Summary

  50. DWDM Benefits • DWDM provides hundreds of Gbps of scalable transmission capacity today Provides capacity beyondTDM’s capability Supports incremental, modular growth Transport foundation for nextgeneration networks

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