1、Introduction to Optical Networking: From Wavelength Division Multiplexing to Passive Optical Networking,Dr. Manyalibo J. Matthews Optical Data Networking Research Bell Laboratories, Lucent Technologies Murray Hill, NJ 07974 USA,University of Tokyo Visit March 22, 2004,T.Harris,A.Harris,M.Matthews,19
2、97,2000,AT&T,Lucent Uber Alles,Lucent A la Carte,1996,2001,spectroscopy,NSOM,Confocaldevice physics network subsystems!,Evolution of Lucent and Matthews/Harris Lab:,Akiyama,Matthews,Tunable Lasers,Telecom Lasers,Semiconductor Laser Device Physics,Quantum Wire Lasers,Outline,Introduction Overview of
3、Optical Networking Types of Networks Fiber, Lasers, Receivers Coarse Wavelength Division Multiplexing Ethernet Passive Optical Networks Conclusions & Future,Emergence of Optical Networks,Mesh Backbone Network,Regional Point of Presence,CO-1,CO-n,Core/Backbone/LongHaul,Regional/Metro,Access/Enterpris
4、e,Local Service Node,Access Node,Passive WDM,Passive WDM,DSL, FTTH,PON,Wavelength Division Multiplexed (WDM) Long-Haul Optical Fiber Transmission System,Transmitter,Transmitter,Transmitter,Receiver,Receiver,Receiver,M U X,D E M U X,Optical Amplifier,l1,l2,l3,WDM “Routers”,Erbium/Raman Optical Amplif
5、ier,Categorizing Optical Networks,DWDM: Dense Wavelength Division Multiplexing (1nm spacing) CWDM: Coarse Wavelength Division Multiplexing (20nm spacing) TDM: Time Division Multiplexing (e.g. car traffic) SCM: Sub-Carrier Multiplexing (e.g. Radio/TV channels) SMF: Single-Mode Fiber (core9mm) MMF: Mu
6、lti-Mode Fiber (core50mm) LWPF: Low-Water-Peak Fiber DCF: Dispersion Compensating Fiber EML: Externally modulated (DFB) laser DFB: Distributed Feedback Laser FP: Fabry-Perot Laser APD: Avalanche Photodiode PIN: p-i-n Photodiode,Optical Fiber Attributes,Attenuation: Due to Rayleigh scattering and che
7、mical absorptions, the light intensity along a fiber decreases with distance. This optical loss is a function of wavelength (see plot).,Dispersion: Different colors travel at different speeds down the optical fiber. This causes the light pulses to spread in time and limits data rates.,Types of Dispe
8、rsion,Chromatic Dispersion is caused mainly by the wavelength dependence of the index of refraction (dominant in SM fibers),Modal Dispersion arises from the differences in group velocity between the “modes” travelling down the fiber (dominant in MM fibers),t,t,t,t,launch,receive,Non-Linear Effects i
9、n Fibers,Self-Phase Modulation: When the optical power of a pulse is very high, non-linear polarization terms contribute and change the refractive index, causing pulse spreading and delay.,Four-wave Mixing: Non-linearity of fiber can cause mixing of nearby wavelengths causing interference in WDM sys
10、tems.,Stimulated Brillouin Scattering: Acoustic Phonons create sidebands thatcan cause interference.,Cross-Phase Modulation: Same as SPM, except involving more than one WDM channel, causing cross-talk between channels as well.,First Window,Second Window,Third Window,ATTENUATION (dB/km),WAVELENGTH (n
11、m),1310nm,1550nm,Attenuation/Loss in Optical Fiber,First Window 850nm High loss; First-gen. semiconductor diodes (GaAs) Second Window 1310nm Lower Loss; good dispersion; second gen. InGaAsP Third Window 1550nm Lowest Loss; Erbium Amplification possible,850nm,First window, second window, third window
12、 correspond (roughly) to first, second and third generation optic network technology,Dispersion Characteristics*,First Window,Second Window,Third Window,DISPERSION COEFF, D (ps/km-nm),WAVELENGTH (nm),Standard SMF has zero dispersion at 1310nm Low Dispersion = Pulses dont spread in time Dispersion co
13、mpensation needed at 1550nm Limits data transmission rate due to ISI (inter-symbol interference) Dispersion not so important at 850nm Loss usually dominates,* Modal dispersion not included,Characterization of System Quality,Bit Error Rate: input known pattern of 1s and 0s and see how manyare correct
14、ly recongnized at output. Eye Diagram: Measure openness of transmitted 1/0 pattern usingscope triggered on each bit.,Eye opening,Effect of Dispersion and Attenuation on Bit Rate,30,10,1,Bit rate (Mb/s),Distance (km),0.1,10,100,1000,10,000,1,1550nm,1310nm,850nm,Dispersion limited,Attenuation limited,
15、single-mode fiber,multi-mode fiber,Coaxial cable,For short reaches (1-2 km), all optics are “Gigabit capable”For longer reaches (10 km), only 1310/1550 nm optics are “Gigabit capable”,20,x,x,Cat 3 limit,Cat 7 limit,Cat 5 limit,x,Twisted Pair,Technology Trends,850nm & 1310nm Preferred by high-volume,
16、 moderate performance data comm manufacturers,1310nm & 1550nm Preferred by high performancebut lower volume (today)telecomm manufacturers,Reason? You need lots of them, they dont need to go far, and youre not using enough fiber ($) to justify wavelength division multiplexing (WDM), I.e. low-quality
17、lasers are OK.,Reason? You dont need lots, but they have to be good enough to transmit over long distances cost of fiber (and TDM) justifies WDM 1550nm is better for WDM,DFB vs. FP laser,Simple FP,mirror,gain,cleave,+,-,mirror,gain,AR coating,+,-,Etched grating,l,l,DFB,FP: Multi-longitudinal Mode op
18、eration Large spectral width high output power Cheap,DFB: Single-longitudinal Mode operation Narrow spectral width lower output power expensive,Fiber Bragg Grating External Cavity Laser for Access/Metro Networks,SHOW PLOTS OF FBG-ECL DATA SHOW PICTURE OF XPONENTS EXTENDED REACH FP,Typical FBG-ECL:,B
19、ell Labs FBG-ECL:,HR,AR,gain,FBG,Lensed tip,T=25C,T=85C,HR,AR,gain,FBG,XB region,T=25, 85C,1-2nm grating,1nm grating,Dl (3dB) typ0.5nm dl/dT 0.01nm/oC,?,(from Xponent Photonics, Inc.),Fiber Bragg Grating External Cavity Laser,FBG-ECL output,Typical FP output, Narrow FBG bandwith limits output Dl1nm
20、for extended reach or WDM applications. Simple design (AR-coated FP, XBR, butt-coupled FBG) Mode-hop free operation over 0-70C,Wavelength Stability of FBG-ECL,CW, 40mA bias,DFB drift 0.1nm/oC FP drift 0.3nm/oC,Filter bandwidths of WDM Mux/Demux,0.8nm (100GHz),100 channels (C+L+S),20nm,18 channels (O
21、,E,S,C,L),3.2nm (400GHz),32-64 channels (C+L+S),DWDM: High channel count, narrow channel spacing Temp-stablized DFBs required Temp-stablized AWGs required (typically),CWDM: Low channel count, large channel spacing Uncooled DFBs can be used Filters can be made athermal,xWDM?: Moderate channel count,
22、moderate channel spacing FBG-ECL or Temp-stablized DFBs required Filters can be made athermal suitable for athermal WDM PON!,1260nm,1610nm,1480nm,1610nm,1480nm,1610nm,Example 1: 10Gbps Coarse WDM,-Used currently in Metro systems (rings, linear, mesh) -Spacing of CWDM grid determined by DFB wavelengt
23、h drift -Current systems limited to 2.5Gbps due to cheaper optics -Possible upgrade to 10Gbps?,CWDM Lasers,16 uncooled, directly modulated CWDM lasers (DMLs)rated for 2.5 Gb/s direct modulation (cheap! - $350 a piece)NRZ-modulation at 10 Gb/s (careful laser mounting; no device selection),CWDM System
24、 Improvement using Electronic Dispersion Compensation,Example 2: Ethernet Passive Optical Networks,NO Active Elements in Outside Plant Enable “triple-play” services Simple & cheap,PON,Headend/CO,Homes/Businesses,Outside Plant,Choices of PONs,Architecture/Layout,Upstream Multiplexing,WDM:simple, expe
25、nsive,TDM: simple, cheap,SCM: complex, expensive,Linear Bus: lossy, fiber lean,Ring: lossy, protected,Simple or Cascaded Star: low loss,OLT=Optical Line Termination (head-end) ONU=Optical Network Unit (user-end),EPON Access Platform,Video/IP Television Voice/IP POTS service High-speed data,Residence
26、,Metro Edge,Voice/IP Services,Broadcast VideoVOD,Management,Metro Network,10G Ethernet Or up to 6 1GbE,EPON,optical splitter,optical splitter,32 subscribers Per EPON,Panther EPON OLT Chassis 1232 384 subscribers Dynamic bandwidth Guaranteed QOS,“premium access”,. . .,12 EPONS,Lucent EPON ONU + Gatew
27、ay,Note on Lasers: -Use DFB at headend (shared) -Use FP at Homes (not shared),DFB,FP,ONU Design,Serial Port,GigE uplink,Packet memory,1.25G BM BiDi Xcvr,Flash (CPU) memory,10/100bT diagnostic port,SERDES (w/CDR),PON,FPGA w/ Embedded mProcessor,“CHILD” BOARD,“PARENT” BOARD,ONU,OLT Design,Serial Port,
28、GigE uplink,Packet memory,1.25G BM BiDi Xcvr,Flash (CPU) memory,10/100bT diagnostic port,SERDES (w/CDR),PON,FPGA w/ Embedded mProcessor,Downstream: continuous, MAC addressed Uses Ethernet Framing and Line Coding Packets selected by MAC address QOS / Multicast support provided by Edge RouterUpstream:
29、 Some form of TDMA ONU sends Ethernet Frames in timeslots Must avoid timeslot collisions Must operate in burst-mode BW allocation easily mapped to timeslots,EPON downstream/upstream traffic,1,2,3,2,1,2,2,3,1,2,3,2,1,2,2,3,1,2,2,OLT,OLT,3,3,O N U,O N U,O N U,O N U,O N U,O N U,Edge Router,ONU: Optical
30、 Network Unit OLT: Optical Line Termination,Edge Router,Control “Gates”,Control “Reports”,PON TDMA BURSTMODE OPTICS,Because upstream transmissions must avoid collisions, each ONU must transmit only during allowed timeslot Transmitting “0”s during quiet time is not allowed! Average “0” power -10 to 5
31、 dBm Summing over 16 ONUs would result in a 1dBm noise floor Distinct from “Bursty” nature of Ethernet TRAFFIC Ethernet transmitters never stop transmitting (Idle characters) CDR circuit at receiver stays locked even when no data is transmitted Besides PONs, other systems use burstmode Wireless Shar
32、ed buses/backplanes Optical burst switched (OBS) systems,BURSTMODE TRANSMITTERS,Tx FIFO,Encoder,Serializer,Transmitter,Data,Clock,Prebias,Physical Media,current,Ith,Optical output,“0”,“1”,Modulation current,“off”, Driving LD below Threshold causes Jitter Off-state -40dBm,BURST-MODE RECEIVERS,PROBLEM
33、 OF FAST CDR LOCKING GAIN LEVELING & DYNAMIC RANGE OF OPTICAL RECEIVER,Rx FIFO,CDR,Limiting Amp,Receiver,Data,Clock,Deserializer,Decoder,Reset,IMPACT ON EFFICIENCY,1460 Bytes,64 Bytes,1:4,OLT,ONU 1,1:8,ONU 2,Upstream Bursts,Cascaded PON,Ethernet,IP,TCP,Throughput Efficiency,Conclusions,Optical Netwo
34、rking getting closer and closer to end user For Metro, CWDM is lowest cost solution, but must be improved to handle 10Gbps PON systems could deploy in mass over next 1-2 years, with EPON one of the leading standards Lasers dominate cost, therefore useful to study physics of low-cost laser structures
35、!,THANK YOU VERY MUCH! (Domo Arigato Gozaimashita!),Spare Slides,SYSTEM PENALITIES in PONs,Attenuation in PONs dominated by power splitters:Dispersion penalty for MLMs (Agrawal 1988)Typical p-i-n receivers w/ 150nA current noise, 1.25Gbps, R1 -27dBm (about 1mW) Typical 1310nm FP lasers 0dBm output p
36、ower (about 1mW),(for worst case, D=6ps/nmkm, L=20km, B=1.25Gbps, s=3nm,(For N=32, L=20km; typically 24-26dB w/ connectors, splices, etc.),MODE PARTITION NOISE EFFECT,Mode Partition Noise is due to fluctuations in individual Fabry Perot modes coupled with optical fiber dispersion. Due to uncontrolle
37、d temperature and wavelength drift in FP diodes, dl/dT 0.3nm/oC, and D(l)S0l, the magnitude of this penalty will change with time. Due to lack of screening of FP mode partition coefficient, k, the magnitude of this penalty will also depend on particular FP!,D (ps/nm.km),l (nm),l0,Bit Rate and Reach
38、Limits due to MPN,Reach dependent on “quality” of laser (k factor) (another) Reason why asymmetry in PONs (e.g., 155/622Mbps) are favored GigE? Worst-case isnt quite fair statistical model shows most fiber-laser combinations, D3ps/nmkm, k0.5.,Power penalty due to MPN given by (Ogawa 1985):,Where k i
39、s the MPN coeficient, dependent on mode power correlations.,REDUCING MPN,Dispersion Compensation at OLT Additional Loss, some cost One-size wont fit all, SMF l0 1300-1325nm High-pass filtering using SOA Low frequency MPN components are partially removed Very low noise FP LD driver Replace FP w/ narr
40、ow-line source DFB is current solution 1310nm VCSEL (high-power) Fiber Bragg Grating ECL also a possibility if cost/integration improves,Structure of WDM MUX/DEMUX (Arrayed Waveguide Grating),(100) Si,B,P-doped v-SiO2,Thermal v-SiO2,P-doped v-SiO2 core, core layer,TM, sy,TE, sx,Input waveguides,Output waveguides,Arrayed waveguides,Star coupler,Types of Lasers & Receivers used for Telecommunications,
