A Linewidth-Tolerant Two-Stage CPE Using a New QPSK-Partitioning Approach and an Enhanced Maximum Likelihood Detection for 64-QAM Coherent Optical Systems

We propose a novel two-stage carrier phase estimation (CPE) algorithm for 64-ary quadrature amplitude modulation (64-QAM) coherent optical systems. It makes use of a new quadrature phase shift keying partitioning (QPSK-partitioning) approach and an enhanced maximum likelihood (ML) detection. 36/64 of the 64-QAM symbols are statistically employed by the modified QPSK-partitioning approach to estimate phase noise in the first stage. The proposed enhanced ML detection is used in the second stage to improve linewidth tolerance performance. The simulation results show that, our proposed VVPE^c1&c2 + EML algorithm can achieve much higher linewidth tolerance performance than the modified V&V + MLE algorithm at high laser linewidth level. A combined laser linewidth symbol duration product as high as 5.6 × 10^-5 is achieved by the proposed two-stage CPE algorithm at a target BER of 1 × 10^-2 with 1 dB SNR sensitivity penalty.