Abstract

We have recently demonstrated a double beam modulation (DBM) method using frequency locked lasers (FLL). The DBM automatically creates a subcarrier upon detection by a photodetector. The subcarrier frequencies can be easily tuned. So far we are able to vary the frequency from several GHz to 15 GHz, which is currently limited by the detector and electronics. Therefore the DBM-FLL modulators are the natural building blocks for the SCM (Sub-Carrier Multiplexing) light-wave system. Using the DBM-FLL modulators), we have demonstrated multi-channel broadband optical communications. Both the digital and analog signal can be transmitted simultaneously on a single fiber. Using close-spaced DBM carriers, all the carriers can be optically amplified. The major advantage of using DBM-FLL for SCM is that very high subcarrier frequency can be achieved (in tens of GHz) and that fiber induced distortions are minimized. Also since FM optical carrier(s) is used, the linearity of the laser diode may be more easily to overcome for analog transmissions. Utilizing the FLL modulator within its modulation limits, any broadband analog signals, such as TV VHF band (lower and upper band plus FM radio), CATV channels, and even TV UHF band, can be readily FM modulated onto these subcarriers. The demodulated signals are directly compatible with standard TV or cable ready receivers. Experimental results will be presented and discussed.

© 1990 Optical Society of America