Coherent Fiber-Optic Transmission Systems: Potentials And Problems

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Abstract
Optical communication systems which use heterodyne or homodyne detection are commonly referred to as coherent systems. These systems provide a significant improvement in receiver sensitivity, leading to a substantial increase in repeater spacing. Heterodyning also allows the frequency domain multiplexing of several hundred or more optical carriers, with very narrow separation, leading to a vast improvement in capacity. However, these systems place very stringent requirements upon the coherence of the lasers used. The semiconductor lasers intended for use in these systems possess both phase and intensity noise, which limit the system performance. We give an overview of the manner and extent to which these problems degrade a coherent transmission system. The resulting requirements on laser linewidth are noted. Techniques for the linewidth reduction of semiconductor lasers, such as external grating loading and injection locking, are reviewed.© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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