Heterodyne ASK multiport optical receivers using postdetection filtering

A theoretical model for heterodyne amplitude-shift-keying (ASK) multiport optical receivers is presented. It applies when the transmitter and local oscillator have significant linewidths. The modeled receiver uses square law detection and postdetection filtering. The model allows for the essentially non-Gaussian character of the probability density function of the noise process at the input of the threshold comparator. Numerical computations are made for the {2×2} multiport receiver. They show that such a receiver can handle laser linewidths on the order of the bit rate with 1.5-dB loss as compared to the ideal heterodyne receiver with zero linewidth