Abstract

Optical heterodyne communication systems promise performance improvement of 10-20 dB compared with direct detection systems.¹ Thus a considerable effort has been devoted to heterodyne systems research.^1-4 It is clear now that the laser phase noise is a major problem in heterodyne communication systems; it broadens the laser linewidth and deteriorates the performance of heterodyne receivers. Therefore, it is generally recognized that narrow linewidth lasers are needed for coherent communications. ^1-5 Furthermore, it is generally agreed that the maximum permissible laser linewidth Δv depends on the system bit rate R and the modulation/demodulation technique employed. However, there is no generally accepted relationship among Δv, R, and the modulation/ demodulation technique employed. For example, Ref. 2 states that Δv should be <0.01R for FSK and ASK systems and <0.001R for PSK systems.

© 1985 Optical Society of America