Fiber Systems Dense Wavelength Division Multiplexing DWDM Alpina

Fiber Systems Dense Wavelength Division Multiplexing (DWDM) Alpina Kulkarni Optical Communications (EE 566) Dr. Paolo Liu Electrical Engineering @ 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 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

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

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)

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

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 980 nm or 1480 nm is injected via the pump laser ► Gains ~ 30 d. B; Output Power ~ 17 d. B ►

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 15200 Metro DWDM Solution ► Lucent Technologies § Lambda. Xtreme Transport § Wave. Star OLS 1. 6 T ► 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 http: //www. cisco. com/univercd/cc/td/doc/product/mels/dwdm_fns. htm [2] Fundamentals of DWDM Technology http: //www. cisco. com/univercd/cc/td/doc/product/mels/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/OEG 20011221 S 0035 [7] Cisco Systems http: //www. cisco. com/en/US/products/hw/optical/ps 1996/products_quick_reference_gui de 09186 a 00800886 bb. 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