Abstract

The characteristics and performance of a light-wave SCM system with multiple beam modulation is described. The microwave sub-carriers are formed automatically by heterodyne transmitters employing multiple laser beams. A 10-channel SCM can be easily fit into a WDM division of 1 nm. Phase-locked loops are used to lock the frequencies of the beams. The relative frequencies of beams, which are locked by monitoring the beat frequencies, are in the tens-of-gigahertz range. They can remain stable within the megahertz range. These SCM channels are identified and demultiplexed by microwave sub-carrier frequencies but not directly by optical wavelengths, thus their exact wavelengths and their stability are less important. A heterodyne transmitter with three frequency-locked beams at sub-carrier frequencies of 21 GHz and 17 GHz and modulation/demodulation of these sub-carrier frequencies with a 1 Gb/s signal have been demonstrated. The sub-carrier frequency can be easily tuned from 3 to 21 GHz. The sub-carrier can be readily extended to higher frequencies by using faster photodetectors. By incorporating SCM within WDM, the capacity can be greatly increased without requiring super stable lasers and high resolution optical filters.

© 1992 Optical Society of America