The impact of fiber dispersion on CNR in 80-channel wideband FM CATV transmission

Conventional lightwave CATV carrier to noise ratio (CNR) is limited by receiver shot noise, and requires the use of high launched powers. An alternative approach which can improve receiver sensitivity while retaining the simplicity of analog transmission is electrical frequency modulation followed by intensity-modulated optical transmission. Wideband FM encoding of the entire multichannel signal onto a single microwave carrier has been demonstrated. Work to date has concentrated on 10 to 40 channel systems using the Japanese channel frequency plan, and the impact of fiber dispersion has not been studied. Here we consider 80-channel North American systems, and examine the effects of fiber dispersion on noise performance using numerical simulation. Linear dispersive fiber propagation creates a nonlinear frequency-dependent channel from FM modulator to demodulator, and precludes analytical techniques for accurate analysis of realistic multichannel systems. We have developed a numerical model, which includes linear fiber propagation, optical receiver shot and thermal noise, as well as laser RIN. Ideal FM modulation and demodulation are used, along with pre-emphasis at 6 dB/oct.