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Fiber Systems Dense Wavelength Division Multiplexing (DWDM) Alpina Kulkarni Optical Communications (EE566) Dr. Paolo Liu Electrical Engineering @ UB
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Brief Overview ► Problems with increasing network demands ► Solutions proposed & their limitations ► Evolution of DWDM ► Technical details ► Drawbacks ► Ongoing Research ► Conclusion
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Growing Network Usage Patterns ► Issues Exponential Exponential increase in user demand for bandwidth ► Doubling ► Doubling of bandwidth requirement every 6-9 months Consistency Consistency in quality of services provided Keeping Keeping the cost of solutions at bay ► Solutions Increase Increase channel capacity: TDM, WDM Statistical Statistical multiplexing of users: Multiple optical fibers
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Another glimpse at the solutions ► WDM ► WDM (Wavelength Division Multiplexing) Use Use of optical fibers to achieve higher speeds Utilize Utilize wavelengths to multiplex users Allow Allow continuous channel allocation per user Increases Increases the effective bandwidth of existing fiber ► TDM ► TDM (Time Division Multiplexing) Slotting Slotting of channels simultaneous users Increasing Increasing bit rate to maximize utilization of given bandwidth
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Limitations of current solutions ► WDM Inefficient Inefficient usage of full capacity of the optical fiber Capability Capability of carrying signals efficiently over short distances only ► Improvements in optical fibers and narrowband lasers Birth of Dense WDM (DWDM) ► TDM Dependency Dependency of Mux-Demux on bit rate Limitations Limitations on bit rates ► how ► how fast can we go? (Decides how small the time slots can be)
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Evolution of DWDM Late 1990’s 1996 DWDM Early 1990’s Narrowband WDM 1980’s Wideband WDM 16+ channels 100~200 GHz spacing 2~8 channels 200~400 GHz spacing 2 channels 1310nm, 1550nm 64+ channels 25~50 GHz spacing
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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
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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
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Capacity Expansion
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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
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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
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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
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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
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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
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References [1] Introducing DWDM http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_fns.htm 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 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 http://www.iec.org/online/tutorials/dwdm [4] Dense Wavelength Division Multiplexing (DWDM) Testing http://www.iec.org/online/tutorials/dwdm_test 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 http://www.eetimes.com/story/OEG20011221S0035 [7] Cisco Systems http://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_gui de09186a00800886bb.html http://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_gui de09186a00800886bb.html http://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_gui de09186a00800886bb.html [8] Lucent Technologies http://www.lucent.com/products/subcategory/0,,CTID+2021-STID+10482- LOCL+1,00.html 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) http://www.nortelnetworks.com/products/01/optera/long_haul/dwdm/http://www.nortelnetworks.com/products/library/collateral/12001.25-03-02.pdfhttp://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
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