M winter d kroushkov and k petermann ieee summer topicals july 2010
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M. Winter, D. Kroushkov, and K. Petermann IEEE Summer Topicals July 2010. Cross-Polarization Modulation in Polarization-Multiplexed Systems. typical DWDM system with a nonlinearity probe. ► CW probe is unaffected by linear effects / SPM ► other channels are 10 Gbps OOK in 50 GHz grid.

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Cross-Polarization Modulation in Polarization-Multiplexed Systems

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M winter d kroushkov and k petermann ieee summer topicals july 2010

M. Winter, D. Kroushkov, and K. Petermann

IEEE Summer Topicals

July 2010

Cross-Polarization Modulation in Polarization-Multiplexed Systems


Cross polarization modulation in polarization multiplexed systems

typical DWDM system with a nonlinearity probe

► CW probe is unaffected by linear effects / SPM

► otherchannelsare 10 Gbps OOK in 50 GHz grid


Cross polarization modulation in polarization multiplexed systems

SOP evolutionTx output (fully polarized)


Sop evolution without amplifier noise

significant nonlinear depolarizationrapid (symbol-to-symbol) fluctuations of the SOP

what is going on and is this a problem?

SOP evolution(without amplifier noise)


Cross polarization modulation in polarization multiplexed systems

► basics

cross-polarization modulation (XPolM)

► statistical models

► XPolM and polarization multiplex

► experiments


Xpolm basics

XPolM basics


Cross polarization modulation in polarization multiplexed systems

XPolM is closely related to XPM


Cross polarization modulation in polarization multiplexed systems

nonlinear polarization effects known since at least 1969 ► e.g. Kerr shutter (Duguay and Hansen, APL, pp. 192+, 1969)

XPolM first described in its „current version“ in 1995 ► Stokes space Manakov equation ► collision of two solitons ► Mollenauer et al., Optics Letters, pp. 2060+, 1995

many-channel formulation in 2006 ► Menyuk and Marks, JLT, pp. 2806+, 2006


Cross polarization modulation in polarization multiplexed systems

Poincaré sphere

probe channel

DWDM interferers

Stokes vector sum

nonlinear rotation


Statistical models

statistical models


Cross polarization modulation in polarization multiplexed systems

► length (intensity) varies due to walk-off►(interferer and probe group velocity differs)

► direction (SOP) varies due to PMD► (interferer and probe birefringence differs)

► both effects are random

various models have been proposed to describe this behavior

(interferer) Stokes vectors are not constant


Cross polarization modulation in polarization multiplexed systems

► Karlsson‘s statistical model (JLT, pp. 4127+, 2006)

► influence on PMD compensation ► mostly two-channel system, no PMD dependence

► diffusion model (Winter et al., JLT, pp. 3739+, 2009)

► SOPs evolve as random walk ► ensemble mean values only

► carousel model (Bononi et al., JLT, pp. 1903+, 2003)

► pump and probe rotate when both carry a mark ► two-channel system, no PMD


Sop distribution resembles diffusion

SOP distribution resembles diffusion


Dwdm power channel threshold for mean probe dop 0 97

DWDM power/channel threshold for mean probe DOP=0.97

► resonant dispersion map, 10 × 10 Gbps OOK interferers► @ 50 GHz spacing


Depolarization of probe vs number of 3 dbm interferers

depolarization of probe vs. number of 3 dBm interferers

► difficult to simulate, expensive to measure► saturates at about 20


Xpolm and polarization multiplex

XPolM and polarization multiplex


Cross polarization modulation in polarization multiplexed systems

a typical PolDM system

► selective upgrade: 10G NRZ » 100G PolDM RZ-QPSK

► fits into 50 GHz grid


Cross polarization modulation in polarization multiplexed systems

detected field at y-Rx:

► otherwise crosstalk occurs from x to y and vice versa

► crosstalk increases with misalignment angle and with►length of field vector

polarization DEMUX must be aligned to PolDM subchannels

(visualization in Jones space)


Cross polarization modulation in polarization multiplexed systems

XPolM causes symbol-to-symbol fluctuations around mean SOP

► cannot be compensated (again like XPM)

modern coherent receivers can handle subchannel SOP changes with PMD time constants

► DCF abuse with a screwdriver: 280 µrad/ns(Krummrich and Kotten, OFC 2004, FI3)


Cross polarization modulation in polarization multiplexed systems

field amplitude at y-Rx

aligned subchannels

interleaved subchannels

time

► crosstalk is never zero because pulses at Rx are no longer RZ

(accumulated GVD, PMD, noise)

interleaving RZ-shaped symbols minimizes crosstalk generation


Cross polarization modulation in polarization multiplexed systems

10 × 10G NRZ interferers w/ 100G PolDM-RZ-QPSK probe

► 256 ps/nm RDPS, 10 interferers, SSMF, no PMD

► power/channel threshold is reduced by up to 2 dB


Cross polarization modulation in polarization multiplexed systems

the statistical ensemble (mean DOP = 0.975)

► DOPs and ROSNRs spread over large range

► for DOPs < 0.98 (0.97), ROSNR penalties become significant


Cross polarization modulation in polarization multiplexed systems

Xie showed how PolDM interferers can cause negligible XPolM compared to single-polarization (PTL, pp. 274+, 2009)

► requires RZ pulse shape and subchannel interleaving

► neighboring half-symbol slots have orthogonal polarization states

► probe SOP oscillates but rotation does not accumulate


Experiments

experiments


Cross polarization modulation in polarization multiplexed systems

► onset of nonlinear penalties at much lower powers

► (near) saturation of penalties for large channel spacing

(van den Borne et al., ECOC, 2004, Mo 4.5.5)


Cross polarization modulation in polarization multiplexed systems

► saturation of penalties for large number of interferers

(Renaudier et al., PTL, pp. 1816+, 2009)


Cross polarization modulation in polarization multiplexed systems

► benefit of PolDM vs. OOK interferers

(Bertran-Pardo et al., OFC, 2008, OTuM5)


Summary

summary


Cross polarization modulation in polarization multiplexed systems

► XPolM in DWDM systems causes depolarization

► diffusion model correctly predicts simulated behavior

► depolarization creates detrimental PolDM crosstalk

► can be reduced by interleaving PolDM subchannels

slides available at http://www.marcuswinter.de/publications/ST2010


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