Abstract
We propose a modified method of constant modulus algorithm (CMA) based on polarization demultiplexing
in Stokes space for polarization demultiplexing (SS-PDM) in optical coherent receivers. SS-PDM can tolerate chromatic
dispersion (CD) and polarization-dependent loss (PDL), but is sensitive to PMD. On the other hand, the CMA with
high-order FIR filters could compensate for polarization-mode-dispersion (PMD) effectively, but suffers from the
singularity problem which results from PDL. Therefore, we use the polarization rotation matrix estimated by SS-PDM to
set the initial center taps of the CMA. The singularity problem of the CMA is avoided effectively in a much wider
range of PDL and its convergence speed is also improved. We demonstrate this modified CMA in a simulation of
100-Gbit/s PDM-QPSK with PDL of 1, 3, and 5 dB, respectively. PDL is emulated by attenuating one polarization
tributary before polarization multiplexing and the interaction between PDL and PMD is ignored. The singularity problem
disappears as expected. Because the tolerance of PDL is affected by DGD, we further investigate the PDL tolerance
under different DGD. Finally, we conduct the simulation of 100-Gbit/s PDM-QPSK with PDL of 3 dB over 3000 km
SSMF and 4000 km SSMF separately. The convergence speed accelerates indeed compared with that of the conventional
CMA.
© 2013 IEEE
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