Fiber Systems Dense Wavelength Division Multiplexing (DWDM) Alpina Kulkarni Optical Communications (EE566) Dr. Paolo Liu Electrical UB

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

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

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

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)

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

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

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

Capacity Expansion

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

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

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

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

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

References [1] Introducing DWDM [2] Fundamentals of DWDM Technology [3] Dense Wavelength Division Multiplexing (DWDM) [4] Dense Wavelength Division Multiplexing (DWDM) Testing [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 [7] Cisco Systems de09186a bb.html de09186a bb.html de09186a bb.html [8] Lucent Technologies LOCL+1,00.html LOCL+1,00.html [9] Nortel Networks: “OPTera Long Haul” & “Metro DWDM” ( & ( [10] Agility Communications