Performance Analysis of Phase Noise Cancellation by Asymmetric CMA for Realizing Affordable Coherent PON Transceivers

We investigate the performance of a phase noise cancellation proposal to overcome the inherent laser linewidth limitation that acts as a key limiting factor in realizing digital signal processing (DSP)-based optical coherent access systems. The proposed cancellation algorithm is evaluated and analyzed through both extensive simulations and experimental studies on coherent 20-Gbit/s quadrature phase-shift keying (QPSK) signals. The use of polarization control based on the constant modulus algorithm (CMA) eliminates the polarization interference, which is a primary factor impacting the cancellation of random phase noise. A unique polarization control scheme with asymmetric CMA is proposed in order to remove the singularity issue created by the standard CMA. Its performance is verified in simulations and experiments. Through experiments that emulate laser linewidth by a phase modulator, it is confirmed that the cancellation algorithm overcomes the inherent limitation on laser linewidth.