Theoretical Analysis of Phase Noise Induced by Laser Linewidth and Mismatch Length in Self-Homodyne Coherent Systems

The intra- and inter-data center links face continuously increasing pressure on the transmission capacity while having to meet strict constraints in cost and power consumption. For such cost-sensitive data center applications, self-homodyne coherent (SHC) system as a promising solution has attracted increasing attention. In this article, the influence of phase noise (PN) for the SHC system is thoroughly analyzed by studying the PN probability distribution characteristic and bit-error rate (BER) performance in theory. The correctness of the theorical PN analysis is also verified by simulation. Further, the PN characteristics in SHC systems are investigated and discussed with and without the implementation of carrier phase recovery (CPR). A unique property is found for SHC systems that the system performance is only related to the product of linewidth and mismatch length, independent of the symbol rate in the absence of CPR. For SHC-16QAM systems, in order to limit the OSNR penalty to below 1-dB, the product of laser linewidth and delay mismatch should be kept below 0.18 MHz · m. Under such a conduciton, no CPR algorithm is reuiqred. Alternatively, in presence of CPR, the phase noise tolerance of SHC and conventional coherent systems are similar.