Abstract
In this thesis we discuss the receiver performance of two types of optical coherent communication system, i.e., homodyne PSK systems and heterodyne CPFSK systems . In the first part of this study, which deals with homodyne PSK systems, we emphasize the effect of signal waveform distortion on system performance, although other effects such as the effects of laser phase noise and shot noise are accounted for . In contrast to the conventional discussion in which the received signal data is a sequence of square pulses, this study for the first time investigates the problem encountered in BPSK homodyne communication systems with Costas PLL's as the received signal data is not a sequence of square pulses but is a sequence of distorted pulses . The signal waveform distortion induces additional amount of phase error variance and henceforth an increase in bit-error rate, resulting in a more stringent laser linewidth requirement . Ths laser linewidth requirement is evaluated here taking into account such an effect of signal waveform distion . Then in the second part, we analyze the system performance of optical CPFSK receivers with AFC loops . The effects of loop gain, bandwidth of IF band-pass filter, and postdetection filters are taken into account . The KL (Karhunen-Loeve) expansion and the GQR ( Gaussian quadure rule ) method are used to deal with the laser phase noise characteristics in computing the bit-error rates . With different closed loop gains, we show the improvement of system performance compared with the system without AFC .