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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 USA University of Tokyo Visit – March 22, 2004

2 spectroscopy,NSOM,Confocal…device physics… network subsystems!
Evolution of Lucent and Matthews/Harris Lab: T.Harris A.Harris M.Matthews 1997 2000 AT&T Lucent ‘Uber Alles’ Lucent ‘A la Carte’ 1996 2001 spectroscopy,NSOM,Confocal…device physics… network subsystems! Akiyama Matthews Tunable Lasers Quantum Wire Lasers Telecom Lasers Semiconductor Laser Device Physics

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

5 Wavelength Division Multiplexed (WDM)
Long-Haul Optical Fiber Transmission System Transmitter l1 Receiver D E M U X l2 M U X Transmitter Receiver l3 Optical Amplifier Transmitter Receiver WDM “Routers” Erbium/Raman Optical Amplifier 2

6 Categorizing Optical Networks
Who Uses it? Span (km) Bit Rate (bps) Multi-plexing Fiber Laser Receiver Core/ LongHaul Phone Company, Gov’t(s) ~103 ~1011 (100’s of Gbps) DWDM/TDM SMF/ DCF EML/ DFB APD Metro/ Regional Phone Company, Big Business ~102 ~1010 (10’s of Gbps) DWDM/CWDM/TDM SMF/ LWPF DFB APD/ PIN Access/ LocalLoop Small Business, Consumer ~10 ~109 (56kbps- 1Gbps) TDM/ SCM/ SMF/ MMF DFB/ FP PIN 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~9mm) MMF: Multi-Mode Fiber (core~50mm) 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. launch receive Types of Dispersion é Chromatic Dispersion is caused mainly by the wavelength dependence of the index of refraction (dominant in SM fibers) t t Modal Dispersion arises from the differences in group velocity between the “modes” travelling down the fiber (dominant in MM fibers) é t t

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. Cross-Phase Modulation: Same as SPM, except involving more than one WDM channel, causing cross-talk between channels as well. 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.

9 Attenuation/Loss in Optical Fiber
0.5 1.0 1.5 2.0 2.5 3.0 First Window Second Window Third Window ATTENUATION (dB/km) 800 900 1000 1100 1200 1300 1400 1500 1600 1700 WAVELENGTH (nm) 850nm 1310nm 1550nm First 850nm High loss; First-gen. semiconductor diodes (GaAs) Second 1310nm Lower Loss; good dispersion; second gen. InGaAsP Third 1550nm Lowest Loss; Erbium Amplification possible First window, second window, third window correspond (roughly) to first, second and third generation optic network technology 6

10 DISPERSION COEFF, D (ps/km-nm)
Dispersion Characteristics* Third Window Second Window -120 -90 -60 -30 3.0 First Window DISPERSION COEFF, D (ps/km-nm) 800 900 1000 1100 1200 1300 1400 1500 1600 1700 WAVELENGTH (nm) 1310nm 1550nm 850nm 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 7

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
Attenuation limited Dispersion limited 30 20 1310nm 850nm 10 1550nm single-mode fiber Distance (km) Coaxial cable multi-mode fiber Cat 3 limit Cat 5 limit Cat 7 limit Twisted Pair 1 x x x 0.1 1 10 100 1000 10,000 Bit rate (Mb/s) For short reaches (1-2 km), all optics are “Gigabit capable” For longer reaches (~10 km), only 1310/1550 nm optics are “Gigabit capable” 1

13 Technology Trends 850nm & 1310nm Ô Preferred by high-volume,
moderate performance data comm 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. 1310nm & 1550nm Ô Preferred by high performance but lower volume (today) telecomm manufacturers 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 9

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

15 Fiber Bragg Grating External Cavity Laser for Access/Metro Networks
Dl (3dB) typ<0.5nm dl/dT ~ 0.01nm/oC Typical FBG-ECL: Lensed tip FBG gain T=25C HR AR T=85C <1nm grating Bell Labs FBG-ECL: XB region T=25, 85C FBG gain ? HR AR 1-2nm grating SHOW PLOTS OF FBG-ECL DATA SHOW PICTURE OF XPONENT’S EXTENDED REACH FP (from Xponent Photonics, Inc.)

16 Fiber Bragg Grating External Cavity Laser
FBG-ECL output Typical FP output • Narrow FBG bandwith limits output Dl~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
DFB drift ~ 0.1nm/oC FP drift ~ 0.3nm/oC CW, ~40mA bias

18 Filter bandwidths of WDM Mux/Demux
0.8nm (100GHz) DWDM: • High channel count, narrow channel spacing • Temp-stablized DFBs required • Temp-stablized AWGs required (typically) 1480nm >100 channels (C+L+S) 1610nm 20nm CWDM: • Low channel count, large channel spacing • Uncooled DFBs can be used • Filters can be made athermal 1260nm 18 channels (O,E,S,C,L) 1610nm 3.2nm (400GHz) xWDM?: • Moderate channel count, moderate channel spacing • FBG-ECL or Temp-stablized DFBs required • Filters can be made athermal • suitable for athermal WDM PON! 1480nm 32-64 channels (C+L+S) 1610nm

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 50W line 47W chip resistor

21 CWDM System Improvement using Electronic Dispersion Compensation

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

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

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

BiDi Xcvr SERDES (w/CDR) GigE uplink Report Generator Packet Memory TX RX Control Parser Demux watchdog0 watchdog1 discovery Periodic generator EPON driver EPON core EPON MAC Mux Timestamp CRC LLID manager Queue GMII SERDES & Optics CPU FPGA “CHILD” BOARD FPGA w/ Embedded mProcessor Packet memory “PARENT” BOARD Flash (CPU) memory 10/100bT diagnostic port Serial Port

26 OLT Design CPU FPGA PON 1.25G BM BiDi Xcvr GigE uplink SERDES (w/CDR)
ONU PON Grant List Gate Generator Packet Memory RTT table TX RX Control Parser Demux watchdog0 watchdog1 discovery Keepalive scheduler EPON driver MPCP driver EPON core MPCP core EPON MAC Mux Timestamp CRC LLID manager Queue RTT Processor Report processor GMII SERDES & Optics Report table CPU FPGA 1.25G BM BiDi Xcvr GigE uplink SERDES (w/CDR) FPGA w/ Embedded mProcessor Packet memory 10/100bT diagnostic port Flash (CPU) memory Serial Port

27 EPON downstream/upstream traffic
1 Control “Gates” 1 2 3 Edge Router OLT 1 2 3 2 O N U 1 2 3 2 2 O N U 1 2 3 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 3 Control “Reports” O N U 1 Edge Router OLT 1 1 2 3 3 2 2 O N U 2 2 2 O N U 3 3 3 ONU: Optical Network Unit OLT: Optical Line Termination

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

Tx FIFO Encoder Serializer Transmitter Physical Media Data Clock Prebias Optical output “1” • Driving LD below Threshold causes Jitter • Off-state ~ -40dBm “0” “off” current Ith Modulation current


31 IMPACT ON EFFICIENCY . Data Upstream Bursts Cascaded PON ONU 2 ONU 1
guardband ONU 1 ONU 2 ONU 1 . ONU 2 1:8 OLT 1:4 Throughput Efficiency Our current situation Standard GE transceivers Burst-mode transceivers Laser on AGC settle CDR lock Byte sync ONU1 payload (Ethernet Frames) off C R D M A S V L N H E T O I F ST P K SM GS W Z U G Q Data 64 Bytes ~1460 Bytes Ethernet IP TCP

32 (Domo Arigato Gozaimashita!)
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

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

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, 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/ l (nm) l0

36 Bit Rate and Reach Limits due to MPN
Power penalty due to MPN given by (Ogawa 1985): Where k is the MPN coeficient, dependent on mode power correlations. 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.

37 REDUCING MPN Dispersion Compensation at OLT
Additional Loss, some cost One-size won’t fit all, SMF l0 ~ nm 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)
waveguides Star coupler Input waveguides Output waveguides P-doped v-SiO2 core TM, sy B,P-doped v-SiO2 } core layer Thermal v-SiO2 TE, sx (100) Si 1

39 Types of Lasers & Receivers used for Telecommunications

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