Mode-partition noise and intensity correlation in a two-mode semiconductor laser

The intensity-noise characteristics of a nearly single-longitudinal-mode semiconductor laser are analyzed by adopting a two-mode model. An approximate solution of the resulting Langevin rate equations is used to obtain an analytic expression for the enhancement of the main-mode intensity noise caused by mode partition. We also obtain analytic expressions for the autocorrelation and cross-correlation functions which are used to discuss noise variances in the two modes. In particular, the cross-correlation function is related to the mode-partition coefficient, a measure of anticorrelation between the two modes that is useful to analyze the system performance. Our results show explicitly how the intensity correlation is affected by the mode-suppression ratio and other device parameters.