Abstract

Significant improvements in the area of long distance and high bit rate single-mode fiber optical communication systems appear to be possible with heterodyne detection. The SNR could be increased by 10-20 dB depending on the modulation format.¹ A heterodyne system requires high stability of the frequency difference between the emitter and the local oscillator. Only slow drifts can be reduced by controlling the laser diode (LD) temperature.^2,3 However, if FSK or coherent PSK modulation are to be fully exploited (as they give the best performance), a high short-term stability is required (~2 MHz peak to peak¹). On the other hand, it would be desirable to directly modulate the LD to avoid the use of an external modulator.

© 1981 Optical Society of America