Abstract

The subcarrier multiplexing (SCM) scheme can be effectively used for optical multiple-access network (OMAN) applications. However, if the conventional direct laser modulation is employed, not only are the modulation frequencies limited by laser, but also the induced fiber dispersion and the laser's own distortion can be serious at high frequencies. Therefore, conventional SCM is not suitable for OMAN. We have recently demonstrated a novel double-beam modulation (DBM) method that uses a frequency- locked laser (FLL). The DBM automatically creates a subcarrier upon detection by a photodetector. Information can be readily modulated onto the subcarrier by simply modulating the laser(s) at the baseband. We have demonstrated information transmission on subcarriers from several gigahertz to 15 GHz. Thus, if we use DBM-FLL to implement the SCM, the frequency limitations and distortion problems are minimized or removed. Because subcarriers in tens of gigahertz can be achieved, the information capacity can be quite large. The network is accessed by means of different subcarrier frequencies. Recent advances in laser-diode technologies have made the realization of DBM-FLL feasible. The frequency-shift-keying digital-modulation characteristics of DBM-FLL and various subcarrier frequency generations and detection schemes are described.

© 1990 Optical Society of America