Interchannel Nonlinearities in Polarization-Multiplexed Transmission

Marcus WinterKlaus Petermann

Hochfrequenztechnik-Photonik

TECHNISCHEUNIVERSITÄTBERLIN

Dario Setti

http://www.marcuswinter.de/publications/ecoc2009

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

cross-phase modulation (XPM)and

cross-polarization modulation (XPolM)

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

XPolM is similar to XPM

nonlinear variation of the

birefringence refractive index

proportional to sum of interfering channel

Stokes vectors powers

results in the modulation of signal

polarization phase

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

XPolM – where and what?

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

systems with large XPM impairment are affected(e.g. selective 10G 40G/100G upgrades)

fully polarized signal becomes depolarized

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

depolarization can be visualized on the Poincaré sphere

quantified by nonlinear DOP reduction

XPolM model exists to predict this magnitude*

* Winter et al., JLT 17 (27), p. 3739, 2009.

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

impairments in PolDM systems

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

single-polarization Tx is replaced by PolDM Tx

Rx signal processing can follow PMD changes, but not XPolM

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

Rx polarization misalignment generates crosstalk between PolDM subchannels

statistically, crosstalk depends only on the degree of polarization and the source amplitude

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

interleaving RZ-shaped symbols minimizes crosstalk amplitude at target sampling instant

even with interleaving, the crosstalk is never zero, but significantly smaller

due to signal distortions, noise, etc.

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

system simulations

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

nonlinear threshold of the NRZ interferers is reduced by 2dB due to XPolM

(1dB when interleaving is used)

10 × 10G NRZ interferers w/ 25Gbaud PolDM-RZ-QPSK probe

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

mean values ► individual distribution

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

ROSNR penalties at 4 dBm NRZ power (mean DOP = 0.961)

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

ROSNR penalties at 3 dBm NRZ power (mean DOP = 0.975)

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

ROSNR penalties at 2 dBm NRZ power (mean DOP = 0.984)

at 2 dBm, fluctuations become comparable toXPM-related spread at 4 dBm

(3 dBm when interleaving is used)

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

summary

TECHNISCHEUNIVERSITÄTBERLIN

ECOC 2009 – Tu.10.3.4

XPolM-induced depolarization leads to crosstalk between PolDM subchannels

interleaving the subchannels can significantly reduce the crosstalk penalty (but not eliminate it)

the mean nonlinear DOP reduction for 25 Gbaud PolDM-RZ-QPSK should not exceed 0.98

the resulting 10G NRZ interferer NLT penalty is up to2 dB over XPM alone