Increasing interest is being shown worldwide in the use of coherent techniques for optical fiber communication systems because of their improved sensitivity and selectivity compared with conventional direct detection systems. These improvements are obtained at the expense of increased system complexity, however, and, in particular, highly coherent sources are required for the transmitter and local oscillator. PSK homodyne systems, for example, have the most stringent requirements and will require laser linewidths between 10 and 100 kHz for reasonable data rates and phase locked loop bandwidths.

© 1986 Optical Society of America

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