Non-negligible loop delay time influence on coherent optical PSK systems performance degradation

The phase-locked loop propagation time is important unavoidable factor for high-speed coherent detection systems. This paper report the linewidths requirements and the power penalties taking into account the loop propagation delay, laser phase noise and shot noise of corresponding photodiodes. The coherent optical receivers with PLL, based on Costas loop or decision-driven loop are taken into consideration for both type of coherent detection (homodyne and heterodyne). The expressions for phase error variance and receiver bit-error rate are determined the most precisely to date and these expressions are used in power penalty determining. Contrary to the present papers, two sources of power penalty creating, the phase error and power splitting, are considered simultaneously, due to their mutual dependency, instead of considering them separately. The optimum loop filter timing constant that gives the minimum phase error standard deviation can be determined from proposed method. The optimum power splitting ratio to minimize the receiver error probability was used in the power penalty determining. The performance comparison between Costas loop and decision-driven loop receivers is given, too.