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PMD and PMD compensation NOBEL WP5 results NOBEL_WP5_PMD_summary_draft_4_extended.ppt Henning Bülow Yu Rong Zhou Alfons Schinabeck Stefano Santoni Andrew Lord Bernd Bollenz Thomas Fischer

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Page 2 PMD / PMDC models Overview PMD / Q dependency Equaliser S (FFE + DFE) Receiver (AT) In-line compensator S E Receiver 1stage/2stage PMDC Receiver (NRZ, CS-RZ, DB) Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE) Independent rules: PMD > threshold OSNR> threshold Table: Q-penalty vs PMD / Q Curve: Q-penalty vs PMD Representation in model PMD orders S: NW simulation E: Experiment PMD: 1st order 1st+2nd multi-order

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Page 3 PMD/Receiver models PMD / Q dependency Equaliser (FFE + DFE) Receiver (AT) In-line compensator Receiver 1stage/2stage PMDC Receiver (NRZ, CS-RZ, DB) see mitigation Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE) Independent rules: PMD > threshold OSNR> threshold Table: Q-penalty vs PMD / Q Curve: Q-penalty vs PMD Representation in model PMD orders PMD: 1st order 1st+2nd multi-order

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Page 4 PMD penalties (all-orders) evaluation EOP evaluation modelling the fiber with the wave plates approach (all-orders PMD) and numerical simulation (Split- Step Fourier method) EOP vs. instantaneous DGD (100,000 realisations) for RZ and NRZ EOP pdf for NRZ and RZ NRZ 10Gb/s outage probabiltiy

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Page 5 PMD penalties (all-orders) evaluation Result (table representation) Q penalty vs. baseline Q for different mean DGD (OP = 10 -5, 10Gb/s NRZ signal)

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Page 6 PMD penalties (all-orders) evaluation Impact of fiber non-linearity Comparison with simulations including non linear (Kerr) effects (0dBm) G.652 (top) and G.655 (bottom) cases NRZ (left) and RZ 30 ps FWHM (right) Comparing EOP due to non linear effects and to PMD (blue line) with EOP due to PMD only (red line): EOP due to non linear effects and to PMD can be linearly added for NRZ signals Cumulative EOP due to non linear effects and to PMD is less than the linear sum of the two independent components, for RZ signals NRZRZ NRZRZ

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Page 7 Comparison of different PMD modelling approaches Analytical model for 1 st order PMD: Q-factor penalty as a function of PMD and outage probability (OP): A: pulse factor, B: bit rate, : mean DGD Comparison of approaches: Wave plate approach (all order PMD) Analytical (1 st order PMD) split-step (1 st order PMD) Good agreement of all different approaches for 10Gb/s NRZ signal Analytic model giving efficient calculation with sufficient accuracy for baseline Q value relevant to system applications

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Page 8 PMD mitigation PMD / Q dependency Equaliser (FFE + DFE) Receiver (AT) In-line compensator Receiver 1stage/2stage PMDC Receiver (NRZ, CS-RZ, DB) Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE) Independent rules: PMD > threshold OSNR> threshold Table: Q-penalty vs PMD / Q Curve: Q-penalty vs PMD Representation in model PMD orders PMD: 1st order 1st+2nd multi-order

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Page 9 PMD mitigation Investigated approaches optical PMDC 1stage 2stage in-line (distributed el. Equalizer FFE+DFE MLSE (=VE) PMD-, Q- thresholds from literatur details on next pages Q-penalty vs. PMD curves and Q-p. vs. (Q,PMD) for FFE+DFE details on next pages

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Page 10 PMD rules with optical compensators (1stage, 2stage) PMD thresholds are based on literature values (10 -5 outage) (multi-order PMD simulations) Near-optimum feedback signal (eye monitor) for 2 stage device Q threshold referenced to ATC receiver (w/o. PMD) PMD threshold Q threshold (referenced to ATC receiver)

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Page 11 PMD in-line mitigation/1 In-line PMD mitigation (optical, bit-rate independent approach) Simulation on EOP and DOP correlation DOP < 0.9 is a condition to limit the penalty below around 2 dB EOP [dB] PMD PMD + CD + NL DOP ECP [dB] EOP [dB] DOP [dB]

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Page 12 PMD in-line mitigation/2 EOP – DOP correlation Possible behaviour of DOP along the link Pulses depolarisation can be caused by both first and second order PMD (in this cases, first order is dominant) PMD PMD + CD + NL

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Page 13 PMD in-line mitigation/3 Compensation at receiver DOP degrades along the link. The energy causing ISI can be no longer discriminated from the energy within the bit slot based on the polarisation. As a consequence, the performance improvement is limited. In-line compensation DOP is maintained high (> 0.9) along the link and pulses are confined in the bit slot 5 x 100 Km EOP [dB]

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Page 14 Physical terminal design Electronic equalisation / Receiver Dynamic electronic signal processing in receiver for PMD / distortion mitigation ensures maximum length optical paths under dynamically changing path conditions in dynamic optical networks Most-likely equalisation schemes identified Feed-forward + decision feedback equal. (FFE+DFE)analog processing Viterbi equaliser (VE, also referred to as MLSE)digital processing FFE + DFE Viterbi equaliser (MLSD)

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Page 15 PMD rules without and with mitigation by electronic equalisers Performance analysed: Q-penalty vs. DGD equalisers: FFE+DFE, VE as reference: Receiver w. adaptive threshold control (ATC) modulation formats: NRZ, duobinary, CSRZ duobinary NRZ VE1 FFE+ DFE CSRZ ATC VE ATC VE Q-penalty vs. DGD (=3xPMD) VE2

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Page 16 PMD rules with mitigation by MLSE MLSE model for network simulation VE with 4 states and 3 ADC bits for 10.7 Gb/s Assumption: PMD 1 st order is the dominant effect for NRZ, ODB, CM-DML Figures show PMD penalty after MLSE related to b-t-b with equaliser for each modulation format Parameter DGD; Chromatic dispersion: 0 ps/nm NRZ ODBCM-DML

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Page 17 PMD rules of FFE+DFE equaliser based on refined PMD model In detail: FFE+DFE equaliser model for 10Gb/s NRZ BER limit trace in 1 st and 2 nd order PMD plane; given PMD, OSNR Integration of outage probability OP; Iteration:OP=10 -5 by OSNR variation Table quantifies: PMD improvement by equaliser / margin DGD/PMD SOPMD/PMD 2 04 4.5 BER= limit CP (BER>limit) pdf of 1st + 2nd order PMD PMD rules for FFE+DFE PMD equaliser

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Page 18 Experimental evaluation of PMDC PMD / Q dependency Equaliser (FFE + DFE) Receiver (AT) In-line compensator Receiver 1stage/2stage PMDC Receiver (NRZ, CS-RZ, DB) Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE) Independent rules: PMD > threshold OSNR> threshold Table: Q-penalty vs PMD / Q Curve: Q-penalty vs PMD Representation in model PMD orders PMD: 1st order 1st+2nd multi-order

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Page 19 PMD-C Measurement results Measurement setup: Measurement results: Compensation possible with the polarizer approach at 10 Gbit Can compensate 4.7 ps mean PMD (2 dB OSNR penalty) Conclusion: System parameters: Modulation format NRZ Bitrate 10.7 Gbit BER w/o FEC 1e-6

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Page 20 Network simulations w. PMD PMD / Q dependency Equaliser (FFE + DFE) Receiver (AT) In-line compensator Receiver 1stage/2stage PMDC Receiver (NRZ, CS-RZ, DB) Equalisers (NRZ, CS-RZ, DB) (FFE+DFE, MLSE=VE) Independent rules: PMD > threshold OSNR> threshold Table: Q-penalty vs PMD / Q Curve: Q-penalty vs PMD Representation in model PMD orders PMD: 1st order 1st+2nd multi-order

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Page 21 Network simulation (RWA) Modeled for standard receivers and for equalisers FFE5+DFE1 Static dimensioning simulations on DT-17nodes network, with random fiber PMD coefficient distribution: Avg. links load with standard Rx:72% Avg. links load with equaliser FFE5+DFE1:79% And consequently the network dimensioning with equaliser results in less node relations Equaliser provides more flexibility in the route selection (more routing options with Q-factor higher than the accepted threshold) thus enabling a more efficient network optimisation.

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Page 22 Network simulations with scaled PMD and with different PMD distribution (and other some pessimistic assumptions) on DT-17 network show blocking due to impairments (no transparent routing possible) Possible approach for impairments-aware RWA including PMDC, Equalisers and 3R Possible extension of RWA to overcome blocking events due to physical impairments Modified Dijkstra algorithm including information on different mitigation methods, together with a strategy to properly assign resources (regenerators, equalisers, PMDCs), trying to maintain transparent routing in a cost-effective way

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Page 23 Algorithm description In its iterative process the Dijkstra routing algorithm starts from a node that is reachable and tries to move to adjacent nodes: in the impairments-aware routing, to consider a node reachable the Q factor shall remain over the selected threshold. Comparison between Q and Q-threshold refers to the total Q-factor of the lightpath segment or to a single component of the Q factor, e.g. Q-penalty due to PMD greater than few dBs). If Q is below the threshold a blocking occurs and, in this case, instead of discarding the path routing under analysis (as in D26 simulations), a possible solution can be selected, among: Putting an equaliser (or any other compensation technique) at the receiver Inserting an in-line PMDC Inserting a Regenerator (no transparent routing, last choice) It should be noted that all the rest of the network is unknown at this point (from the algorithm point of view) and decisions on how to solve possible Q-related blocking is not optimal, since cannot be based on the knowledge of the whole path/network In case all of the listed solutions can solve the blocking, the iterative Dijkstra process can continue. In order not to select just one solution (that in few next steps can become apparently the ‘worst’ one) all the three possible solutions are kept and independently ‘propagated’ with proper ‘labelling’ in order to keep trace of them For each kind of label (Regen, PMDC, EQUAL), in case a certain node is reached with different paths the path with the best Q-factor is selected. Since this procedure applies independently for each label, a certain node can be reached from a subpath ‘x’ adopting Regen and with subpath ‘y’ adopting PMDC The multiple labelling is kept and propagated till another blocking event occurs: in this case a single solution to solve the previous blocking has to be selected (otherwise the alternatives can grow exponentially), according to a predefined rule (e.g. minimum cost) and the same process applies. As a final result a single lightpath can be routed, for instance, with a regenerator and a couple of in-line PMDCs, or with any other combination. At this point a post-analysis can be performed in order to optimise Regenerators/PMDCs placement

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Page 24 Network example/1 A Z lightpath Q > QthresholdQ < Qthreshold Comparison between Q and Qthreshold could refer to the total Qfactor of the lightpath segment or to a single component of the Q factor (e.g. Qpenalty due to PMD greater than few dBs) A Z A Z A Z Equaliser at RX In-line PMDC Regenerator To overcome the blocking, one among the three approaches below can be chosen ij ij ij ij Label type Q < Qthreshold Q > Qthreshold Node not yet reached

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Page 25 Network example/2 A Z A Z A Z Equaliser at RX In-line PMDC Regenerator In case some solutions experience a further block while others are still valid, they are no longer considered. When only one solution remains, it is ‘promoted’ to permanent Q < Qthreshold ‘promoted’ to permanent solution i i i j j jk k k

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Page 26 Network example/4 in case more than one subpath with the same label reach a node, the subpath associated to the best Q will be selected and further propagated x iy w Label type Q- factor Other Info on subpath 26 Predecessor,… 22 Predecessor,… 21 Predecessor,… Label type Q- factor Other Info on subpath 24 Predecessor,… 25 Predecessor,… 22 Predecessor,… Label type Q- factor Other Info on subpath 23 Predecessor,… 24 Predecessor,… 24 Predecessor,… Label type Q- factor Other Info on subpath 26 Predecessor x,… 25 Predecessor y,… 24 Predecessor w,…

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Page 27 Preliminary considerations Possible approach for impairments-aware RWA including PMDC, Equalisers and 3R This procedure only applies to static network dimensioning. Extension to dynamic dimensioning requires further evaluations This method fits with heuristic approaches as the multi-layer graph RWA adopted in D26 The method does not reach an optimum solution, but a post-elaboration with optimisation is possible (once the preferred path has been chosen, actual placement of PMDC/Regenerator can be optimised and some over-dimensioning removed) Mixing up different mitigation techniques, some configurations resulting form the algorithm could need further analysis Modelling of some components (e.g. PMDC) not yet available for implementation of the RWA algorithm. Moreover the computation of Qpenalty due to PMD in the different configurations should take into account other mitigation techniques possibly applied on the path In principle more solutions can be included (different mitigation solution at receiver can be computed, provided that a proper modelling in term of Q-factor is available)

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