Optical Performance Monitoring Applications in Transparent Networks Dan Kilper Advanced Photonics Research Lucent Technologies dkilper@lucent.com C. R. Giles, W. Weingartner, A. Azarov, P. Vorreau, and J. Leuthold WOCC April 22, 2005 Newark, NJ 1
Old Technology Ultra-long Transport Systems Point-to-Point Transparency Current End 4000km at 10Gb/s End Terminal >2000km at 40Gb/s Terminal (opaque) (opaque) OA Repeaters ROADM ROADM Mitigation of: Advanced Technologies: Noise Raman Amplification Dispersion Dispersion Managed Solitons Gain variation Dynamic Gain Equalization Nonlinearity DPSK, Advanced Modulation Formats SEA MIN NY DEN CHI KC WA SF LA ATL DAL HOU 2
ULH+ROADM/OXC MESH NETWORK ULH+ROADM/OXC MESH NETWORK C ET N E W λ 10 λ 11 λ 12 S λ 4 λ 5 ET ET MOADM B A λ 1 λ 2 λ 3 λ 4 λ 5 λ 6 λ 7 λ 1 λ 2 λ 3 λ 7 λ 12 λ 10 λ 11 λ 6 Operational Complexity + Advanced Technology D ET � Advanced Monitoring Transparent Reconfiguration • Intersecting lines must discover one another and exchange topology information. • Auto-provisioning must operate across the mesh network. • Faults are correlated across multiple systems. • Greater flexibility requires better stability & control 3
Optical Network Performance Monitoring • First Generation: Total power monitoring. Amplifier gain adjustment, signal presence, link status verification. • Second Generation: WDM channel presence / power and wavelength. T O Auto-provisioning and gain flattening. D A Y • Third Generation: Channel optical SNR / Q-factor, active dispersion compensation. Fault isolation, dispersion compensation. • Fourth Generation: Transparent network management. Channel performance verification after link concatenation. • Fifth Generation: In-situ link parameter extraction from detailed channel signatures. Preplanning / preprovisioning assessment. Resource database creation. 4
Eliminating Regenerators 500 km 500 km 600 km OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO 1600+ km DGEF OEO OEO OEO OEO OEO OEO OADM OEO OEO OEO OEO OPM OPM • Must also consider fault management requirements • Cost of OADM/ULH technology (DGEF)/OPM < OEO 5
3G: DWDM Fault Management OEO OEO OEO OEO OEO OEO OADM OADM OEO OEO OEO OEO OPM OPM OPM OPM OPM OPM OPM OPM OPM Locate degradation: Read out OPM history: Report BER dispatch maintenance compare actual performance degradation with stored reference • Advanced technologies/network complexities – Component alarms may be insufficient • Need OPM that correlates with end terminal BER – OPM registers change when end terminal BER alarm triggers • OPM granularity to suit carrier opex goals 6
Electronic Fault Management 500 km 500 km 600 km OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO BER OSNR: Distance • BER monitoring is sufficient – No errors in: No errors out – Noise does not propagate past regenerators • Isolate faults to ~600 km 7
Ultra-Long Haul Transmission 1800+ km OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OPM OPM OPM Error Free OSNR: Error Free Distance • Replace OEOs with OA repeaters: lose fault isolation • BER at OA repeaters has limited benefit • Noise propagates through repeaters 8
Fault Isolation Fault Metrics: 35 10 dB BER drop 10 -9 BER threshold 30 ‘Good’ Fault Location OSNR (dB) 25 ‘Impaired’ 20 BER: 10 -12 15 10 -9 10 5 10 15 20 25 30 Node # • Need sensitivity to wide variety of impairments. BER 10 -9 gives ~ 4 orders of magnitude • advanced warning in FEC-based links. 9
OPM Fault Management Technologies • BER Measurement – Sensitive to end terminal impairments – Problem: BER in network better than end term. Q Factor • Noise loaded BER measurement – Sensitivity close to BER • Other methods: OSNR, half-clock, pol. ext., histograms, tones, autocorrelation, … – Must show advantage over Q/BER approach • Cost/sensitivity/impairment coverage – Target systems that cannot use Q-factor 10
Q Factor • Signal to Noise Ratio Measurement 10G RZ Eye Diagram µ − µ Signal 1 0 = → Q µ 1 σ + σ Noise σ 1 1 0 V th µ 0 σ 0 µ − µ − V V ( ) 1 th 0 th 1 = + BER V erfc erfc th 4 σ σ 2 2 1 0 11
Q Factor Monitoring Techniques (A) Variable threshold, dual decision – eye mapping (B) Variable threshold, use FEC/integrate data (C) (C) Asynchronous histogram methods • Sensitivity questions Asynch. V thr (D) Sampling techniques part (A) (B) (D) V thr V ref 12
FEC Error Count Eye Mapping • Vary voltage threshold across center of eye • Use commercial 10 Gb/s receiver -2 Low OSNR High OSNR -3 -4 Log(BER) -5 -6 -7 -8 -9 -10 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Decision Level (Volts) 13
Q-factor vs. time • Determined measurement noise contributions under different conditions • Error due to counting statistics, threshold voltage accuracy, power fluctuations 20 19 18 Q-factor (dB) 17 Variable Vary OSNR Decision 16 Level Fixed 15 Decision Level 14 13 0 2000 4000 6000 8000 10000 Time (sec) 14
Dispersion map issues … … +300 ps/nm node Distance -300 ps/nm ∆ Q sensitivity is • Q factor varies with dispersion map weakly dependent • 10Gb/s: up to 1000 ps/nm on magnitude of – OK for trend monitoring Q factor • 40 Gb/s: eye closed until end terminal – Would need per-channel DCM/tunable DCM – Also obstacle to 40G optical networks 15
OSNR/Dispersion 21 20 19 • Measure Q-Factor up Q-Factor (dB) 18 to –982 ps/nm accum. 17 dispersion 16 15 • OSNR sensitivity only 14 13 weakly dependent on 0 ps/nm 12 dispersion -512 ps/nm 11 -982 ps/nm Use DCMs & SSMF 10 9 to add dispersion 8 14 16 18 20 22 24 26 28 30 32 34 OSNR (dB) 7 0 ps/nm |Q meas - Q bkgd | (dB) -512 ps/nm 6 -982 ps/nm 5 Dispersion managed solitons: pulses retain 4 shape throughout 3 transmission! 2 • Always within receiver 1 Q-factor range 0 10 15 20 25 30 35 OSNR (dB) 16
Sensitivity varies with monitor location • OSNR, non-linear impairments accumulate with distance Calculate “optical” Q on line: • Dispersion follows map Monitor independent: 32 Pre-compensation: 30 I D -I 0 ps/nm P 1 0 Q = ( ) -300 ps/nm 28 2 2 2 σ D + σ + σ Beat P ASE ASE -500 ps/nm 26 -800 ps/nm Q 2 (dB) 24 Dispersion Penalty OSNR 22 Drop ( ) 2 BER: 20 D D f P = 1 A 10 -14 18 D A =Accum. Dispersion 10 -9 16 f = scaling factor 14 (4 dB @ 800 ps/nm) 12 0 5 10 15 20 25 30 Span # 17
Dispersion faults +/- 624 ps/nm for • Strongly dependent on map 10 -9 BER degradation • Look for discontinuities along path • Use +/- bands to identify dispersion problems +624 ps/nm 32 Pre-compensation: 30 -800 ps/nm 28 Slope changes in Q trend 26 2 (dB) 24 22 Q -624 ps/nm 20 18 16 14 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Span # 18
Performance Polling: Tunable Filter + OA Span loss ~ 20 dB Filter OA -20 dB Q Q O/E O/E P Tap P • Guarantee equal or better sensitivity than end terminal • Replace entire OEO terminal with single OE, channel selector, and single channel OA • O/E provides BER, conventional PM, Q-factor, average power, channel presence, wavelength drift 19
WDM vs. (O)TDM WDM: Access signals with OE throughout system OEO OEO OEO OEO OEO OEO OADM OEO OEO OEO OEO OE: Q OE: Q OTDM: OE not available/feasible within network OEO OEO OTDM OEO O3R OADM OEO OEO OPM? OPM? 20
QoS Monitoring in Transparent Networks Quality of Service (QoS): per channel BER 500 km 400 km 600 km OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO PM O3R How do we monitor in OPM OEO an all-optical network? PM O3R OPM OEO PM O3R OPM 21
Regeneration Applications • Unambiguous indication of signal quality – Correlation with common impairments • Do not need to isolate or measure impairments • No contingencies on relative impairment contributions • Absolute measure of signal quality – Usually only coarse measure • Error free/not error free • Guarantee above threshold: 10 -14 BER • Satisfy operating requirements of system – System specific: input power, modulation format, etc. 22
Optical Regeneration + Monitoring λ 1 CW λ 2 SOA Data λ Filter P cv 2 P data For given input power: more or less power will arrive at the output depending on the input signal quality and the filter characteristics 23
Unambiguous Quality Indicator: P out /P in Dispersion Noise 1.0 1.0 Monitor Signal (a.u.) 0.8 0.6 0.8 0.4 0.2 0.6 0.0 12 14 16 18 20 22 24 26 28 30 -150 -100 -50 0 50 100 150 OSNR (dB) Dispersion (ps/nm) Unable to isolate noise or dispersion But.... Monitoring signal decreases with decreasing signal quality 24
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