40Gb/s & 100Gb/s Transport in the WAN Dr. Olga Vassilieva Fujitsu Laboratories of America, Inc. Richardson, Texas

Outline Introduction Challenges of 40Gbps transmission Modulation formats for 40Gbps Advanced optical technologies enabling 40Gbps From 40Gbps to 100+Gbps Summary 1 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Introduction Today s networks deploy 2.5Gbps and 10Gbps line rates Networks will migrate to 40Gbps (and in the future to 100Gbps) per wavelength High demand for transmission capacity Higher rate client interfaces Technologies to support 40Gbps transmission Advanced modulation format Tunable Chromatic Dispersion Compensator (TDC) Tunable lasers 40Gbps networks must co-exist with today s networks 2 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Supporting 40Gbps Transmission Same transmission quality as 10Gbps systems Challenges associated with 40Gbps solution: OSNR requirement increases by 6 db Chromatic dispersion tolerance decreases (1/16-th of 10G system) PMD tolerance decreases (1/4-th of 10G system) Same network connectivity as 10Gbps Challenges: Sensitivity to OADM filtering increases Example of optical spectra 40 Gbit/s NRZ signal 10 Gbit/s NRZ signal 80 GHz 20 GHz 3 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Increasing Channel Capacity channel spacing Power Power λ 1 λ 2 λ 3 crosstalk 10 Gbit/s Optical spectrum λ 40 Gbit/s Optical spectrum 3 channels at 10 Gbit/s Channel spacing: λ 3 channels at 40 Gbit/s Channel spacing: λ (same) Crosstalk between channels Power cut off Transmittance of optical filter λ 40 Gbit/s Optical spectrum λ Spectrum degradation due to cascaded ROADM filter devices Solution: New Modulation Formats with improved spectral efficiency. 4 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Light Properties to Modulate Intensity Phase Phase (Frequency) Polarization Modulate one or more light properties Intensity modulation (on-off keying): Widely used modulation technique for up to 10Gbps transmission Easy to modulate and easy to detect Phase modulation: Well known technique but was not used in optical communications Detection is more difficult compared to on-off keying Polarization modulation: Relatively new technique Detection is difficult 5 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Non Return-to-Zero (NRZ) LD Transmitter MZM 43 Gb/s Data out NRZ Eye diagram Optical spectrum π/2 0 π/2 Intensity 1 1 0 1 0 Phase time Intensity modulation format Widely used at 10Gb/s Simplest Tx and Rx configuration The optical spectrum has a carrier NRZ has medium width optical spectrum 6 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Carrier-Suppressed Return-To-Zero (CS- RZ) LD Transmitter MZM 43 Gb/s Data NRZ 21.5 GHz Clock out 21.5 GHz Clock CS-RZ Eye diagram Optical spectrum Phase π/2 0 π/2 π Intensity 1 1 0 1 0 Intensity 1 1 0 1 0 Phase time 0 time Intensity modulation format CS-RZ Tx requires additional clock modulation 7 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc. Pulse train has RZ shape with alternate π phase shifts between consecutive bit slots The optical spectrum has a suppressed carrier High tolerance to non-linear effects Higher receiver sensitivity than NRZ Y. Miyamoto et al., in Proc. OAA 99, vol. PdP4, 1999.

Duobinary Modulation Format 43 Gb/s Data 43 Gb/s Data π 0 Intensity Transmitter Precoder Precoder LD LPF MZM LPF 1 1 0 1 0 Phase time out Duobinary Eye diagram Intensity modulation format Complicated Tx design: Requires data pre-coder and low pass filter (LPF) Optical spectrum Pulse train has NRZ shape with some residual light within 0 symbols Narrow optical spectrum Increased spectral efficiency and Large chromatic dispersion tolerance Poor receiver sensitivity: 3 db worse than NRZ Poor non-linear tolerance K. Yonenaga et al., J. Lightwave Technol., vol. 15, No. 8, pp. 1530-1537, 1997. 8 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Return-to-Zero Differential Phase Shift Keying (RZ-DPSK) LD 43 Gb/s Data π π Intensity Intensity Transmitter PM Precoder DPSK 1 1 0 1 0 Phase 0 time 1 1 0 1 0 Phase 0 time 43 GHz or 21.5 GHz Clock 43 GHz or 21.5 GHz Clock RZ-DPSK Eye diagram Phase modulation format Tx requires two modulators: Phase Modulator (PM) and Intensity Modulator (IM) Pulse train has RZ shape 9 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc. Optical spectrum 3 db Rx sensitivity advantage over NRZ High tolerance to non-linear effects Y. Miyano et al., in Proc. OECC 2000, vol. 14D3-3, 2000.

Return-to-Zero Differential Quadrature Phase Shift Keying (RZ-DQPSK) LD 21.5 Gb/s Data 21.5 Gb/s Data π/2 PM Transmitter Precoder Precoder PM DQPSK 21.5 GHz or 10.75 GHz Clock RZ-DQPSK out 21.5 GHz or 10.75 GHz Clock Eye diagram Optical spectrum Intensity 1 1 0 1 0 7π/4 Phase 5π/4 3π/4 π/4 time Intensity 1 1 0 1 0 7π/4 Phase 5π/4 3π/4 π/4 time Four level phase modulation Reduced line rate by 50% compared to DPSK: increased spectral efficiency, PMD and Chromatic dispersion tolerance More complex transmitter design: two phase modulators and one intensity modulator Pulse train has RZ shape Optical spectrum is narrow Has ~3 db Rx sensitivity advantage over NRZ R.A. Griffin et al., in Proc. OFC 2002, WX6, 2002. 10 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Tolerance to OADM Concatenation Signal spectrum Before filtering Cumulative transmission window Signal spectrum After 24 OADM nodes Power (20 db/) T T f f OADM OADM OADM T f Power (20 db/) Frequency (50GHz/) Frequency (50GHz/) Before filtering After 16 OADMs After 24 OADMs NRZ CS-RZ RZ-DPSK RZ-DQPSK 11 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Optical Noise Tolerance of 40Gbps Signals Simulation results NRZ Duobinary 4.5 db 7 db RZ-DPSK RZ-DQPSK Both RZ-DPSK and RZ-DQPSK have high OSNR tolerance 12 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

PMD Tolerance of 40Gbps Signals 3 Simulation results 43 Gbit/s 2.5 Q penalty (db) 2 1.5 1 NRZ RZ-DPSK RZ-DQPSK 0.5 0 0 5 10 15 20 25 30 35 DGD (ps) RZ-DPSK exhibits two times larger PMD tolerance than NRZ due to RZ pulse carving RZ-DPQSK exhibits even larger tolerance due to halved symbol-rate 13 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Optical Nonlinearity Tolerance of 40Gbps Signals Q penalty (db) Simulation results: SMF 4 spans x 50 km 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0-0.5 Duobinary NRZ RZ-DPSK CS-RZ RZ-DQPSK Duobinary -6-5 -4-3 -2-1 0 1 2 3 4 5 6 Fiber input power (dbm/ch) NRZ CS-RZ RZ-DPSK RZ-DQPSK Advanced modulation formats such as CS-RZ, RZ-DPSK and RZ- DQPSK show high tolerance to non-linear effects 14 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Chromatic Dispersion Tolerance Q-penalty (db) 5 4 3 2 1 0-1 NRZ CS-RZ Optical duobinary CSRZ-DPSK RZ-DQPSK -2-300 -200-100 0 100 200 300 Residual dispersion (ps/nm) RZ-DQPSK and Duobinary show CD high tolerance 15 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

40 Gbps Modulation Formats : Advantage NRZ Duobinary CS-RZ RZ-DPSK Tx out MZI out RZ-DQPSK Tx out MZI out : Disadvantage 1 Phase= π 0 Phase= 0 4 values are mapped to phase 0, π/2, π, 3π/2 Optical spectra Optical noise tolerance Chromatic dispersion tolerance PMD tolerance Optical nonlinearity tolerance OADM filtering tolerance Frequency (GHz) Frequency (GHz) Frequency (GHz) Frequency (GHz) Frequency (GHz) poor medium poor medium medium very poor good (in linear regime) medium poor good medium medium medium good medium very good medium medium good medium RZ-DQPSK is attractive in many aspects for high bit-rate transmission good good good good good 16 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

40Gbps RZ-DQPSK RZ-DQPSK is the best modulation format to enable 40Gbps transmission Superior filtering tolerance Multiple passes through ROADMs Superior CD tolerance Can support 40Gbps WDM transmission over existing networks Superior PMD tolerance and OSNR performance Longer transmission spans, fewer regeneration sites and increased number of ROADM nodes per network 17 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Advanced Technologies to Support 40Gbps Transmission Optical transmitter Transmission line Optical receiver Tunable laser modulator Optical amp VDC PD CDR FEC Device Tunable laser source Modulator Variable dispersion compensator (VDC) High-speed electronic devices High performance error correction technology Characteristic Narrow spectral linewidth & full-band tunability Generates 40Gbps signal Operates at any wavelength in entire band with small pass-band effects Devices for modulator drivers, preamp, and CDR (clock and data recovery) Extended transmission distance with minimal bit rate increase 18 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

LiNbO3 Modulators for 40Gb/s 40 Gb/s low drive voltage DQPSK LN optical modulator Ultra low 4.0 V drive voltage 25 GHz bandwidth Compact size Integration of phase modulators RZ-DQPSK DATA CLOCK PM π/2 PM 19 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

40Gb/s RZ-DQPSK Transceiver Module Modulation format: RZ-DQPSK C- and L-band fully tunable Multi rate: 43 Gb/s, 44.6 Gb/s SFI-5, 300pin MSA interface Size: 320mm x 110mm x 40mm Low power consumption: 35 W BER 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 RZ-DQPSK transceiver 10 12 14 16 18 20 22 24 Optical SNR (db) NRZ transceiver 4.5 db 4.5 db noise tolerance improvement from NRZ format 2.8x transmission distance 20 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

40Gb/s RZ-DQPSK Transceiver Performance Degradationofsignalquality[dB] Degradation of signal quality [db] 2.5 2.0 1.5 1.0 0.5 0.0 Binary modulation about 8 times Measured Calculated Binary modulation: 100 km DQPSK DQPSK: 810 km Measured Calculated 0 500 1000 1500 Transmission distance estimated by PMD tolerance [km] (in case of PMD coefficient 0.2 ps/ km) Transmission reach limited by PMD was found 8 times better than that of standard binary modulation Longer spans and fewer regeneration sites 21 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Variable Dispersion Compensation for 40Gbps Virtually Imaged Phased Array Component 3-D mirror y z Optical circulator Collimating lens Glass plate x Cylindrical lens 2 Line-focus lens Cylindrical lens 1 Transmission grating Chromatic dispersion in 40Gbps systems More severe dispersion tolerance ~ 50 ps/nm 1/16 of 10G systems Chromatic dispersion changes with temperature ~60 ps/nm @ 600 km, 50 C change 22 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc. Advantages of available Variable Dispersion Compensation Replaces menu of fixed DCM High tunable dispersion resolution: 1 ps/nm Large variable dispersion range: ± 800 ps/nm No penalty due to fiber nonlinear effect

Deployment Strategies of 40Gbps Green field deployment Deployment of new 40Gbps DWDM systems Upgrade of already installed 10Gbps DWDM systems* Add 40Gbps line cards to existing 10Gbps DWDM Utilize the same existing transmission infrastructure Same fibers Same dispersion compensating modules (DCM) Same optical amplifiers Same OADM nodes (same OADM filtering properties) R. Fiorone et al., in Proc. OCOC 2004, Th.2.5.4, 2004. 23 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Upgrade of Existing 10Gbps Networks Migration to 40Gbps is very simple thanks to currently developed 40Gbps technologies such as: New spectrally efficient modulation formats (i.e. DQPSK) Variable dispersion compensation Simply add 40Gbps line cards to existing 10Gbps networks Increase transmission capacity w/o installation of new networks No changes to existing infrastructures cost savings! No impact on 10Gbps signals 10Gbps and 40Gbps signals can co-exist in the same network! 24 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Transmission IEEE 802.3 HSSG is considering multiple approaches Short haul connections Typically 300-1000 meters for inter-switch links in data centers. Current proposals: 4x CWDM, 5x, 10x parallel Medium-range interface ~ 10 Km, 40Km Current Proposals: 4x, 5x parallel, 1x serial Question: How to transport 100GE in DWDM networks? Parallel Transport on multiple wavelengths Requires synchronization of wavelengths due to differential propagation delay Manage a band of wavelengths Simpler Tx/Rx, but low fiber utilization Serial Transport on single wavelength Complex Tx/Rx Higher spectral efficiency Higher total transport capacity over a WDM system Transmission impairments 25 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Transmission Impairments at 100Gbps Transmission impairments are very severe at 100G: Chromatic dispersion tolerance decreases (1/100-th of 10Gb/s system) PMD tolerance decreases (1/10-th of 10G system) OSNR requirement increases by 10dB Today s networks are mostly designed for 100 GHz ITU grid Sensitivity to OADM filtering increases Counter-measures Advanced multi-level modulation formats Low symbol rate Adaptive CD compensation Forward error correction (FEC) Coherent detection PMD and CD tolerance can be further improved 26 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Serial Transmission How to transport 100GE serially in DWDM networks? 4 (e.g. POLMUX QPSK) 10G elec. bit/symbol 2 1 (RZ/NRZ) 10G elec. QPSK 20G elec. (RZ/NRZ) 40G elec. (A) Increase data rate OR 10G 40G 160G Data Rate (b/s) (B) Multi-level modulation ( X bits per symbol) 27 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Serial Transmission (OTDM) Various 100Gbps serial optical transmission experiments have been performed: (1) Optical time division multiplexing (OTDM) (480km DMF) Pros: Low speed electronics Cons: Requires short-pulse laser source Transmitter tends to be bulky and expensive Complex signal processing at the transmitter and receiver Operation on 100GHz ITU grid is not feasible 8x 12.5 Gb/s data Short-pulse laser MZM MZM MZM OTDM-MUX 8x12.5 -> 100 Gb/s 100 Gb/s NRZ w/1:2 DEMUX Rx R. Derksen et al., in Proc. OFC 2006, PDP37, 2006. 28 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Serial Transmission (ETDM) (2) Electrical time division multiplexing (ETDM) 107 Gbps NRZ or Duobinary transmission 100G electronics is not a mature technology Cons: Bandwidth limitation of electro-optical modulator and receiver Operation on 100GHz ITU grid is not feasible 2x 50 Gb/s data 2:1 mux LD 100 Gb/s data MZM 100 Gb/s NRZ or Duobinary w/1:2 OTDM demux Rx P.J. Winzer et al., in Proc. OCOC 2005, PD paper Th4.1.1, 2005. C.R. Doerr et al., in Proc. OCOC 2005, PD paper Th4.2.1, 2005. 29 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Serial Transmission (DQPSK) (3) DQPSK is a good candidates for 100+Gbps transmission Pros: Symbol rate 50Gbaud/s Lower speed electronics (50Gbps) Relaxed CD, PMD and OSNR tolerance Operation on 100GHz ITU grid is feasible Cons: Higher complexity of transmitter/receiver 2x 50 Gb/s data 2x 50 Gb/s O/E LD PM PM 50 Gbaud DQPSK Demodulator O/E O/E M. Daikoku et. al, OFC 2006, PDP36. 30 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Serial Transmission (POLMUX DQPSK) (4) POLMUX DQPSK is another candidate (A) 100Gb/s Low speed electronics (25Gbps) Operation on 100GHz ITU grid is feasible PMD limited reach and CD tolerance increases due to doubled symbol duration LD (B) 160Gb/s 2x 25 Gb/s el. driver RZ mod V PBS H 2x 25 Gb/s el. driver 2x 44 Gb/s el. driver LD RZ mod 31 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc. PM PM PM PM I Q I Q Polarization mux V PBC H 2pol x 25 Gbaud C.R.S. Fludger et. al, OFC 2007, PDP22. V PBS H 2x 44 Gb/s el. driver PM PM PM PM I Q I Q Polarization mux PBC H A.H. Gnauck et. al, OCOC 2006, Th4.1.2. V 2pol x 44 Gbaud Optical diverse coherent receiver* 90 o O/E ADC Hybrid O/E ADC PBS LD Polarization alignment 4x 25 Gb/s O/E 90 o Hybrid Direct detection receiver O/E O/E V PBS H ADC ADC Digital Signal Processor 4x 44 Gb/s O/E DI O/E O/E DI O/E Delay Interferometer

100+ Gbps Champion Experiments When Experiment Distance Company Paper ECOC 2005 107Gb/s Duobinary ETDM Tx, OTDM Rx - Alcatel-Lucent Th.4.1.1 ECOC 2005 107Gb/s NRZ ETDM Tx and OTDM Rx - Alcatel-Lucent Th.4.2.1 OFC 2006 10x107 Gb/s NRZ transmission 400 km Alcatel-Lucent PDP32 OFC 2006 100Gb/s DQPSK 50 km KDDI-NICT-Sumitomo PDP36 OFC 2006 100Gb/s NRZ ETDM Rx 480 km HHI-Siemens-Micram PDP37 ECOC 2006 10x107Gb/s ETDM NRZ OTDM Rx 1000 km Alcatel-Lucent Tu.1.5.1. ECOC 2006 10x107Gb/s RZ-DQPSK transmission 2000 km Alcatel-Lucent Th.4.1.3 ECOC 2006 140x111Gb/s PDM-CSRZ-DQPSK 160 km NTT Th.4.1.1 OFC 2007 10x107 Gb/s NRZ-DQPSK transmission 1,200 km Alcatel-Lucent PDP24 OFC 2007 10x107 Gb/s NRZ transmission 480 km Alcatel-Lucent PDP23 OFC 2007 10x111Gb/s PDM-RZ-DQPSK 2,375 km CoreOptics-Siemens PDP22 OFC 2007 204x111Gb/s PDM-CSRZ-DQPSK 240 km NTT PDP20 32 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

100+ Gbps Transmission 100+ Gbps transmission is possible with: Multi-level modulation (I.e. QPSK) Polarization multiplexing Adaptive CD compensation FEC Coherent detection PMD and CD tolerance can be further improved Advantages of using QPSK: Low speed electronics Relaxed CD, PMD and OSNR tolerance due to low symbol rate Operation on 100GHz ITU grid is feasible due to narrower optical spectrum Compatibility with existing networks 33 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.

Summary Discussed 40Gbps enabling technologies Advanced modulation formats Tunable lasers Variable Chromatic Dispersion Compensator RZ-DQPSK has the best CD, PMD performance and filtering tolerance Universal solution to 40Gbps Metro/LH applications 40Gbps channels can be added to 10Gbps infrastructures without any change of existing networks Transition from 40G to 100+G is possible with DQPSK Thank you! 34 All Rights Reserved, 2007 Fujitsu Laboratories of America, Inc.