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Fiber Systems Dense Wavelength Division Multiplexing (DWDM)

Fiber Systems Dense Wavelength Division Multiplexing (DWDM). Alpina Kulkarni Optical Communications (EE566) Dr. Paolo Liu Electrical Engineering @ UB. Brief Overview. Problems with increasing network demands Solutions proposed & their limitations Evolution of DWDM Technical details

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Fiber Systems Dense Wavelength Division Multiplexing (DWDM)

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  1. Fiber SystemsDense Wavelength Division Multiplexing (DWDM) Alpina Kulkarni Optical Communications (EE566) Dr. Paolo Liu Electrical Engineering @ UB

  2. Brief Overview • Problems with increasing network demands • Solutions proposed & their limitations • Evolution of DWDM • Technical details • Drawbacks • Ongoing Research • Conclusion

  3. Growing Network Usage Patterns • Issues • Exponential increase in user demand for bandwidth • Doubling of bandwidth requirement every 6-9 months • Consistency in quality of services provided • Keeping the cost of solutions at bay • Solutions • Increase channel capacity: TDM, WDM • Statistical multiplexing of users: Multiple optical fibers

  4. Another glimpse at the solutions • TDM (Time Division Multiplexing) • Slotting of channels  simultaneous users • Increasing bit rate to maximize utilization of given bandwidth • WDM (Wavelength Division Multiplexing) • Use of optical fibers to achieve higher speeds • Utilize wavelengths to multiplex users • Allow continuous channel allocation per user • Increases the effective bandwidth of existing fiber

  5. Limitations of current solutions • TDM • Dependency of Mux-Demux on bit rate • Limitations on bit rates • how fast can we go? (Decides how small the time slots can be) • WDM • Inefficient usage of full capacity of the optical fiber • Capability of carrying signals efficiently over short distances only • Improvements in optical fibers and narrowband lasers • Birth of Dense WDM (DWDM)

  6. Evolution of DWDM 64+ channels 25~50 GHz spacing Late 1990’s 16+ channels 100~200 GHz spacing 1996 DWDM Early 1990’s Narrowband WDM 2~8 channels 200~400 GHz spacing 1980’s Wideband WDM 2 channels 1310nm, 1550nm

  7. What is DWDM? • Definition • Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character

  8. How does DWDM fair better? • No O-E-O required • Protocol & Bit Rate independence • Increased overall capacity at much lower cost • Current fiber plant investment can be optimized by a factor of at least 32 • Transparency • Physical layer architecture  supports both TDM and data formats such as ATM, Gigabit Ethernet, etc. • Scalability • Utilize abundance of dark fibers in metropolitan areas and enterprise networks

  9. Capacity Expansion

  10. Basic Components & Operation • Transmitting Side • Lasers with precise stable wavelengths • Optical Multiplexers • On the Link • Optical fiber • Optical amplifiers • Receiving Side • Photo detectors • Optical Demultiplexers • Optical add/drop multiplexers

  11. Optical Amplifier • Eliminates O-E-O conversions • More effective than electronic repeaters • Isolator prevents reflection • Light at 980nm or 1480nm is injected via the pump laser • Gains ~ 30dB; Output Power ~ 17dB

  12. Drawbacks • Dispersion • Chromatic dispersion • Polarization mode dispersion • Attenuation • Intrinsic: Scattering, Absorption, etc. • Extrinsic: Manufacturing Stress, Environment, etc. • Four wave mixing • Non-linear nature of refractive index of optical fiber • Limits channel capacity of the DWDM System

  13. Ongoing Developments • Nortel Networks • Metro DWDM • OPTera Long Haul 5000 Optical Line System • Cisco Systems • ONS 15200 Metro DWDM Solution • Lucent Technologies • LambdaXtreme Transport • WaveStar OLS 1.6T • Agility Communications & UC Santa Barbara • Tunable Lasers used for multiple wavelengths

  14. Conclusion • Robust and simple design • Works entirely in the Optical domain • Multiplies the capacity of the network many fold • Cheap Components • Handles the present BW demand cost effectively • Maximum utilization of untapped resources • Best suited for long-haul networks

  15. References [1] Introducing DWDM http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_fns.htm [2] Fundamentals of DWDM Technology http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_ovr.htm [3] Dense Wavelength Division Multiplexing (DWDM) http://www.iec.org/online/tutorials/dwdm [4] Dense Wavelength Division Multiplexing (DWDM) Testing http://www.iec.org/online/tutorials/dwdm_test [5] “Fiber-Optic Communications Technology” by D.K. Mynbaev, L.L. Scheiner, Pearson Education Asia, 2001 edition [6] “Dense wave nets' future is cloudy” by Chappell Brown, EETimes http://www.eetimes.com/story/OEG20011221S0035 [7] Cisco Systems http://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_guide09186a00800886bb.html [8] Lucent Technologies http://www.lucent.com/products/subcategory/0,,CTID+2021-STID+10482-LOCL+1,00.html [9] Nortel Networks: “OPTera Long Haul” & “Metro DWDM” (http://www.nortelnetworks.com/products/01/optera/long_haul/dwdm/) & (http://www.nortelnetworks.com/products/library/collateral/12001.25-03-02.pdf) [10] Agility Communications http://agility.com/intervals/index.phtml?ID=93&f_code=1

  16. Thank You!

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