Widely Linear Filtering for Multiimpairment Compensation in Dispersion
Managed mQAM Modulated Optical Systems
Abstract
We propose a blind joint equalization algorithm for M-QAM signals based
on a widely linear filtering approach. The proposed scheme jointly
compensates receiver IQ imbalance and polarization mixing, along with
carrier recovery, followed by transmitter IQ imbalance compensation. We
first investigate the proposed scheme’s tolerance to transceiver IQ
Imbalance, polarization mixing, phase noise and frequency offset through
numerical simulations for 32 GBd PM-16QAM and PM-64QAM signals and
compare its performance with the conventional digital processing
algorithms. Further, with the proposed algorithm, we experimentally
demonstrate the improvement in Q2 value to up to
~ 1.22 dB for a 32 GBd PM-16QAM and ~
3.72 dB for a 16 GBd PM-64QAM signal with a phase imbalance of
9o. We show that the MSE convergence of the proposed
joint equalizer is much faster than conventional DSP algorithms.
Deployment of such an equalizer in optical communication systems is
beneficial due to its improved tolerance to multiple impairments, albeit
with increased complexity.