The effects of laser phase noise on the performance of coherent optical fiber communication systems

The negative effects of laser phase noise on the performance of carrier phase estimation and choosing optimized modulation formats for optical coherent communication systems are analyzed.Simulation results show that: For 16-QAM coherent optical fiber communication systems,star constellation has higher tolerance on laser phase noise than that of square constellation because the position of the points in star constellation can be changed according to the properties of system noises;the length of symbol blocks for averaging in the algorithm of Viterbi-Viterbi carrier phase estimation is inversely proportional to the value of laser phase noise;at a certain BER,the required bit number of analog-to-digital converters in optical coherent receivers does not depend on the modulation formats and their levels.