Analysis of relative intensity noise in semiconductor lasers and its effect on subcarrier multiplexed lightwave systems

It is found that the presence of the asymmetric nonlinear gain causes the longitudinal modes of a Fabry-Perot laser as well as a nearly single-mode laser to couple such that the low-frequency relative intensity noise is greatly enhanced. For the first time we have included this asymmetric mode coupling to adequately model the translation of the enhanced low-frequency noise to the signal band of a subcarrier multiplexed transmission system in the presence of both modulation and fiber dispersion. This effect, which is crucial in determining the system's signal-to-noise ratio, is also verified experimentally. Theoretical and experimental investigations of system impairment caused by noise translation and fiber dispersion are also performed. Excellent agreement between the theoretical predictions and the experimental results is obtained.