An optical heterodyne detection system, which has a substantially high receiver sensitivity and precise frequency selectivity, is attractive because it can realize a long-span high-capacity (with frequency division multiplexing) optical transmission system. Particularly, an optical FSK heterodyne single-filter detection system is promising because it can tolerate the spectral spread of a laser diode and can eliminate external modulator insertion loss.1

© 1986 Optical Society of America

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