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Introduction to Optical Networking: From Wavelength Division Multiplexing to Passive Optical Networking Dr. Manyalibo J. Matthews Optical Data Networking.

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Presentation on theme: "Introduction to Optical Networking: From Wavelength Division Multiplexing to Passive Optical Networking Dr. Manyalibo J. Matthews Optical Data Networking."— Presentation transcript:

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

2 T.HarrisA.HarrisM.Matthews 19972000 AT&TLucent ‘Uber Alles’Lucent ‘A la Carte’ 19962001 spectroscopy,NSOM,Confocal…device physics… network subsystems! Evolution of Lucent and Matthews/Harris Lab: Akiyama Matthews Tunable Lasers Telecom Lasers Semiconductor Laser Device Physics Quantum Wire Lasers

3 Outline Introduction Overview of Optical Networking –Types of Networks –Fiber, Lasers, Receivers Coarse Wavelength Division Multiplexing Ethernet Passive Optical Networks Conclusions & Future

4 Emergence of Optical Networks Optical Line System OLS 40/80G OLS 400G 800G/1.6T Mesh Backbone Network Regional Point of Presence CO-1 CO-n Core/Backbone/LongHaul Regional/Metro Access/Enterprise EPON node Metro DMX Local Service Node Metro Edge Switch Metro Edge Switch Optical Cross Connect Metro DMX Access Node Passive WDM C/DWDM Metro Edge Switch DSL, FTTH PON

5 Wavelength Division Multiplexed (WDM) Long-Haul Optical Fiber Transmission System Transmitter Receiver MUXMUX DEMUXDEMUX Optical Amplifier 1 2 3 WDM “Routers” Erbium/Raman Optical Amplifier

6 Categorizing Optical Networks Who Uses it? Span (km) Bit Rate (bps) Multi- plexing FiberLaserReceiver Core/ LongHaul Phone Company, Gov’t(s) ~10 3 ~10 11 (100’s of Gbps) DWDM/ TDM SMF/ DCF EML/ DFB APD Metro/ Regional Phone Company, Big Business ~10 2 ~10 10 (10’s of Gbps) DWDM/ CWDM/T DM SMF/ LWPF DFBAPD/ PIN Access/ LocalLoop Small Business, Consumer ~10~10 9 (56kbps - 1Gbps) TDM/ SCM/ SMF/ MMF DFB/ FPPIN 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 (core~9  m) MMF:Multi-Mode Fiber (core~50  m) 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

7 Optical Fiber Attributes Attenuation:Due to Rayleigh scattering and chemical 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 Dispersion 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 é é launch receive

8 Non-Linear Effects in 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 systems. Stimulated Brillouin Scattering:Acoustic Phonons create sidebands that can cause interference. Cross-Phase Modulation:Same as SPM, except involving more than one WDM channel, causing cross-talk between channels as well.

9 80090010001100120013001400150016001700 0.5 1.0 1.5 2.0 2.5 3.0 First Window Second Window Third Window ATTENUATION (dB/km) WAVELENGTH (nm) 1310nm1550nm 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 correspond (roughly) to first, second and third generation optic network technology

10 Dispersion Characteristics* 1310nm1550nm 850nm 80090010001100120013001400150016001700 -120 -90 -60 -30 0 3.0 First Window Second Window Third Window DISPERSION COEFF, D (ps/km-nm) WAVELENGTH (nm) Standard SMF has zero dispersion at 1310nm –Low Dispersion => Pulses don’t spread in time Dispersion compensation 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

11 Characterization of System Quality Bit Error Rate:input known pattern of ‘1’s and ‘0’s and see how many are correctly recongnized at output. Eye Diagram:Measure ‘openness’ of transmitted 1/0 pattern using scope triggered on each bit. ‘Eye opening’

12 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 limitedAttenuation limited 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

13 Technology Trends 850nm & 1310nm Ô Preferred by high-volume, moderate performance data comm manufacturers 1310nm & 1550nm Ô Preferred by high performance but lower volume (today) telecomm manufacturers Reason? You need lots of them, they don’t need to go far, and you’re not using enough fiber ($) to justify wavelength division multiplexing (WDM), I.e. low-quality lasers are OK. Reason? You don’t 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

14 DFB vs. FP laser Simple FP mirror gain cleave + - mirror gain AR coating + - Etched grating DFB FP: Multi-longitudinal Mode operation Large spectral width high output power Cheap DFB: Single-longitudinal Mode operation Narrow spectral width lower output power expensive

15 Fiber Bragg Grating External Cavity Laser for Access/Metro Networks SHOW PLOTS OF FBG-ECL DATA SHOW PICTURE OF XPONENT’S EXTENDED REACH FP Typical FBG-ECL: Bell 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  (3dB) typ<0.5nm  d  d  nm/ o C ? (from Xponent Photonics, Inc.)

16 Fiber Bragg Grating External Cavity Laser FBG-ECL output Typical FP output Narrow FBG bandwith limits output  ~1nm for extended reach or WDM applications. Simple design (AR-coated FP, XBR, butt-coupled FBG) Mode-hop free operation over 0- 70C

17 Wavelength Stability of FBG-ECL CW, ~40mA bias DFB drift ~ 0.1nm/ o C FP drift ~ 0.3nm/ o C

18 Filter bandwidths of WDM Mux/Demux 0.8nm (100GHz) >100 channels (C+L+S) 20nm 18 channels (O,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, moderate channel spacing FBG-ECL or Temp-stablized DFBs required Filters can be made athermal suitable for athermal WDM PON! 1260nm1610nm 1480nm1610nm 1480nm1610nm

19 Example 1: 10Gbps Coarse WDM -Used currently in Metro systems (rings, linear, mesh) -Spacing of CWDM ‘grid’ determined by DFB wavelength drift -Current systems limited to 2.5Gbps due to cheaper optics -Possible upgrade to 10Gbps?

20 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) 2.5-Gb/s DML 50  line  chip resistor

21 CWDM System Improvement using Electronic Dispersion Compensation

22 Example 2: Ethernet Passive Optical Networks NO Active Elements in Outside Plant Enable “triple-play” services Simple & cheap IP Video Services PSTN Internet PON Headend/CO Homes/Businesses Outside Plant

23 Choices of PONs Architecture/LayoutUpstream Multiplexing OLT … ONU OLT WDM:simple, expensive TDM: simple, cheap SCM: complex, expensive Linear Bus: lossy, fiber lean Ring: lossy, protected OLT ONU Simple or Cascaded Star: low loss ONU OLT=Optical Line Termination (head-end) ONU=Optical Network Unit (user-end)

24 EPON Access Platform Video / IP Television Voice/IP POTS service High-speed data Residence Metro Edge Voice/IP Services Business Broadcast Video VOD Management Metro Network Data 10G Ethernet Or up to 6  1GbE EPON optical splitter optical splitter 32 subscribers Per EPON Panther EPON OLT Chassis 12  32  384 subscribers Dynamic bandwidth Guaranteed QOS “premium access”...... 12 EPONS Lucent EPON ONU + Gateway Note on Lasers: -Use DFB at headend (shared) -Use FP at Homes (not shared) DFB FP

25 ONU Design Report Generator Packet Memory TX RX Control Parser Demux watchdog0 watchdog1 discovery Periodic Report generator EPON driver EPON core RX TX EPON MAC Mux Timesta mp CRC LLID Memory manager Queue manager GMII SERDE S & Optics CPUFPGA 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  Processor “CHILD” BOARD “PARENT” BOARD

26 ONU Grant List Gate Generator Packet Memory RTT table TX RX Control Parser Demux watchdog0 watchdog1 discoveryKeepalivescheduler EPON driverMPCP driver EPON core MPCP core RX TX EPON MAC Mux Timesta mp CRC LLID Memory manager Queue manager RTT Processor Report processor GMII SERDE S & Optics Report table CPUFPGA OLT 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  Processor

27 Downstream: continuous, MAC addressed –Uses Ethernet Framing and Line Coding –Packets selected by MAC address –QOS / Multicast support provided by Edge Router Upstream: 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 1232 1 22 3 1232 1 22 3 1232 1232 1232 1 2 2 OLT 3 3 33 ONUONU ONUONU ONUONU ONUONU ONUONU ONUONU Edge Router ONU: Optical Network Unit OLT: Optical Line Termination Edge Router Control “Gates” Control “Reports”

28 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 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 –Shared buses/backplanes –Optical burst switched (OBS) systems

29 BURSTMODE TRANSMITTERS Tx FIFOEncoderSerializerTransmitter Data Clock Prebias Physical Media current I th Optical output “0” “1” Modulation current “off” Driving LD below Threshold causes Jitter Off-state ~ -40dBm


31 IMPACT ON EFFICIENCY ~1460 Bytes64 Bytes CRCCRC DMACDMAC SMACSMAC VLANVLAN HLENHLEN TOSTOS LENLEN IDID O F ST TTLTTL PROTPROT C H K SM SIPSIP DIPDIP ACKACK HLENHLEN F L A GS WSZEWSZE C H K SM URGURG SPTSPT DPTDPT SEQSEQ Data 1:4 OLT ONU 1 1:8 ONU 2... Upstream Bursts Cascaded PON guardband ONU 1 ONU 2 EthernetIPTCP Laser on AGC settle CDR lock Byte sync ONU1 payload (Ethernet Frames) Laser off Throughput Efficiency Our current situation Standa rd GE transc eivers Burst-mode transceivers

32 Conclusions Optical Networking 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! THANK YOU VERY MUCH! (Domo Arigato Gozaimashita!)

33 Spare Slides

34 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, R~1  -27dBm (about 1  W) Typical 1310nm FP lasers  0dBm output power (about 1mW) (for worst case, D=6ps/nmkm, L=20km, B=1.25Gbps,  =3nm (For N=32, L=20km; typically ~ 24-26dB w/ connectors, splices, etc.)

35 MODE PARTITION NOISE EFFECT Mode Partition Noise is due to fluctuations in individual Fabry Perot modes coupled with optical fiber dispersion. Due to uncontrolled temperature and wavelength drift in FP diodes, d /dT ~ 0.3nm/ o C, and D( )~S 0, 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) 0

36 Bit Rate and Reach 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 isn’t quite fair… statistical model shows most fiber-laser combinations, D<3ps/nmkm, k<0.5. Power penalty due to MPN given by (Ogawa 1985): Where k is the MPN coeficient, dependent on mode power correlations.

37 REDUCING MPN Dispersion Compensation at OLT –Additional Loss, some cost –One-size won’t fit all, SMF 0 ~ 1300-1325nm High-pass filtering using SOA –Low frequency MPN components are partially removed Very low noise FP LD driver Replace FP w/ narrow-line source –DFB is current solution –1310nm VCSEL (high-power) –Fiber Bragg Grating ECL also a possibility if cost/integration improves

38 Structure of WDM MUX/DEMUX (Arrayed Waveguide Grating) (100) Si B,P-doped v-SiO 2 Thermal v-SiO 2 P-doped v-SiO 2 core } core layer TM,  y TE,  x Input waveguides Output waveguides Arrayed waveguides Star coupler

39 Types of Lasers & Receivers used for Telecommunications

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