Abstract

Subcarrier multiplexing (SCM) at microwave frequencies is potentially a practical and economical system for local area network (LAN) and integrated services network (ISN). We have been experimenting with subcarrier light-beam modulation using laser diode self-pulsation. We have been able to narrow the linewidth and to frequency modulate information onto the subcarrier. Our methods may be used to form an SCM system if consistent operation can be attained. We believe that this may be possible by controlling the laser fabrication process. Under certain conditions, a semiconductor laser will show self-sustained pulsation when saturable absorber is incorporated into the laser cavity or, more generally, in an inhomogeneously pumped structure. Here, we use this self-pulsation as the subcarrier for information transmission. The advantage of our SCM scheme is that information channels can be readily frequency modulated and demodulated. As a practical example, the demodulated signals can be made directly compatible with television. When it is compared to the conventional SCM, our scheme is simpler and more cost-effective. A V-channeled substrate inner-stripe (VSIS) laser was used in our experiment, and it showed the self-pulsation to be 2–4 GHz. We have demonstrated the transmission and reception of five television channels with 200 and 400 MHz modulations. Also, by implementing an optoelectronic feedback loop we can achieve much narrower subcarrier linewidth and, hence, higher signal-to-noise ratio. The experimental implementations and results will be presented.

© 1990 Optical Society of America