Impact and compensation techniques of laser phase noise in ultra-dense coherent access networks

The purpose of this paper is to provide a performance comparison between two carrier phase recovery (CPR) algorithms used to mitigate the impact of the laser phase noise in an ultra-dense wavelength-division multiplexing passive optical network WDM-PON (UDWDM-PON) scenario. The algorithms used in this work are the classic non-data-aided (NDA) phase estimation (PE) algorithm based on Viterbi & Viterbi (V&V) method, and another one based on data-aided (DA) technique which makes use of pilot symbols. The performance of the algorithms is numerically assessed for Quadrature Phase Shift Keying (QPSK) and Differential QPSK (DQPSK) modulations formats. The obtained results show that the linewidths of the optical network unit (ONU) and optical line terminal (OLT) lasers play an important role in the system performance. It is shown that fine laser linewidths ofΔν.T_s = 3×10^-4 are required in order to obtain low penalties.