Subcarrier multiplexing (SCM) presents an attractive alternative to timedivision (TDM) or wavelength-division multiplexing (WDM) in lightwave multiple-access networks. In subcarrier systems, data from each channel are used to modulate (ASK, PSK, or FSK) a microwave subcarrier, which is then used to intensity modulate an optical carrier. A high-speed photodetector receives the sum of all transmitted subcarrier channels, and the desired channel is selected with a microwave bandpass filter or rf heterodyne receiver. Each receiver need only have the bandwidth of an individual channel, not the total system bandwidth, whereas receivers for TDM systems require enough bandwidth for the entire data throughput. This reduced bandwidth can lead to a significant increase in receiver sensitivity.
© 1987 Optical Society of AmericaPDF Article