Costas loop analysis for coherent optical receivers

A homodyne Costas loop receiver is analyzed taking both shot and laser phase noise sources into acount. The reciever performance is compared with that of a heterodyne receiver using an electrical Costas loop and that of a coherent receiver using a pilot carrier phase-locked loop. It is shown that, to avoid large performance penalties, beat linewidth to bit-rate ratios smaller than 0.05 percent and 0.5 percent are needed for PSK homodyne and heterodyne systems, respectively.