Coherent optical PSK systems with balanced PLL receivers for nonlinear PLL model

Using the nonlinear second order PLL model the performance of the coherent optical PSK systems with balanced PLL receivers is considered in this paper. The shot noise of the corresponding photodiodes and the data-to-phaselock crosstalk are described through the signal-to-noise ratio in the loop bandwidth, while the laser phase noise is described through the normalized frequency fluctuations instead of the phase ones. The performance comparison between the linear and nonlinear second order PLL model is given and the approximation error is assessed. The theory and results presented here can be applied for analyzing and optimizing the performance in the region where the linear PLL model is not good enough.