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9. WDM

9. WDM. 9.1 Fundamentals 9.2 Devices 9.3 Specific Management. 9.1 FUNDAMENTALS (I). What Is WDM? WDM = Wavelength Division Multiplexing WDM = Optical FDM (Frequency Division Mux.) Fiber capacity is dramatically increased. 9.1 FUNDAMENTALS (II). Characteristics

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9. WDM

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  1. 9. WDM 9.1 Fundamentals 9.2 Devices 9.3 Specific Management

  2. 9.1 FUNDAMENTALS (I) • What Is WDM? • WDM = Wavelength Division Multiplexing • WDM = Optical FDM (Frequency Division Mux.) • Fiber capacity is dramatically increased

  3. 9.1 FUNDAMENTALS (II) • Characteristics • Several light carriers (different λs) in the same fiber • Scalabitity • Usually in C band (1530-1565 nm) → EDFAs • Transparent: no conversions, no formatting • Inexpensive • WDM uses optical devices

  4. 9.1 FUNDAMENTALS (III) • WDM / OTDM (Optical Time Domain Multiplexing) • OTDM: Technology limits speed → limits capacity • WDM: More λs → more capacity • Longer distances between repeaters • Easier add and drop • Cheaper

  5. 9.1 FUNDAMENTALS (IV) • Types of WDM (I) • DWDM: Dense WDM • CWDM: Coarse WDM

  6. 9.1 FUNDAMENTALS (V) • Types of WDM (II)

  7. 9.2 DEVICES (I) • System Block Diagram VOA DCM EDFA DCM EDFA VOA Services Mux (Muxponder) Services Mux (Muxponder)

  8. Optical Add/Drop Mux. (OADM) 9.2 DEVICES (II) • Components (I) l1 l1...n 850/1310 15xx l2 l3 Transponder (O-E-O conversion) Optical Multiplexer l1 l1 l1...n l2 l2 l3 l3 Optical Demultiplexer

  9. 9.2 DEVICES (III) • Components (II) Optical Amplifier (EDFA) Optical Attenuator (Variable OA) Dispersion Compensator (DCM / DCU)

  10. lc Power Power lc l l 9.2 DEVICES (IV) • Components (III) • Optical source: DFB Laser (Distributed FeedBack) • Narrower spectrum • More wavelength stability • Photodetectors: wide band (to cope with several wavelengths) Normal LD DFB LD

  11. 9.2 DEVICES (V) • EDFA (I) • Concept • OF doped with Erbium • Receives pump light at 980 or 1480 nm • Only works in 1510-1600 nm band

  12. 9.2 DEVICES (VI) • EDFA (II) • Characteristics • Optical amplifier (no electrical conversion, no regeneration) • Flat gain in 1530-1565 nm: 20-40 dB • Optical power: 100 mW • Very useful in WDM • Applications • Power stage • In-line amplifier • Wide band amplifier (WDM)

  13. 9.2 DEVICES (VII) • EDFA (III)

  14. 9.2 DEVICES (VIII) • EDFA (IV)

  15. 9.2 DEVICES (IX) • EDFA (V)

  16. 9.3 SPECIFIC MANAGEMENT (I) • Disp. Compensation in WDM • Normal DCF/DCU is not enough: channels accumulate disp. • Channels are to be demux., and then compensated

  17. 9.3 SPECIFIC MANAGEMENT (II) • Nonlinear Management • In general • WDM uses high power levels → problems arise • Power levels should be maintained below safe thresholds • FWM • WDM has many λs and high power levels → problems arise • Regular ITU Grid places intermod. products at nominal λs • It is preferable to use an irregular grid, with lower power levels

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