Fundamental Limit on the Maximum Number of Channels in a Subcarrier- Multiplexed, Lightwave CATV System.

A fundamental limit on the maximum number of channels in a subcarrier-multiplexed lightwave CATV system is derived by considering a totally idealized link consisting of a shot-noise- limited receiver and a laser transmitter with a linear light- versus-current characteristic. Since this characteristic cannot go negatively, there is still the possibility of nonlinear distortion due to clipping. For example, for standard analog VSB-AM TV transmission with the desired 55 dB of total SNR, this fundamental limit is only 50 channels per milliwatt of received optical power. The situation is slightly worse (by about 0.3 dB) if an ideal external modulator is used at the transmitter.