Abstract

As more video services are proposed by the CATV industry, the technological challenge for lightwave engineers is to expand the capacity of subcarrier-multiplexed transmission systems. If a system satisfies the noise and distortion requirements of AM-VSB format, the most stringent, then it is usable for all modulation formats. We have built and tested a system for lightwave transmission of 112 channels. The minimum optical modulation depth (OMD) per channel is set by the carrier-to-noise-ratio (CNR) requirement of the system and so depends on the noise of the system: the laser, transmission medium, and receiver. For a given OMD per channel, the limit on the number of channels is set by distortion caused by a nonlinear light-current characteristic and clipping of the time signal. For typical present-day analog lasers, the number of AM-VSB channels is limited to 60-80. The channel limit can be increased by using multiple lasers. The band of channels can be split into sub-bands, with each sub-band converted into lightwave by its own transmitter. If the system linearity and noise requirements can be met at several wavelengths, then wavelength-division-multiplexing (WDM) can be used to reduce the number of fibers required.

© 1992 Optical Society of America