  We present a new stochastic differential equation model for the spontaneous
emission noise and carrier noise in semiconductor lasers. The correlations
between these two types of noise have often been neglected in recent studies of
the effects of the noise on the laser dynamics. However, the classic results of
Henry show that the intensity noise and the carrier noise are strongly
negatively correlated. Our model demonstrates how to properly account for these
correlations since the corresponding diffusion coefficients agree exactly with
those derived by Henry. We show that in fact in the correct model the
spontaneous emission noise and the carrier noise are driven by the same Wiener
processes. Furthermore, we demonstrate that the nonzero correlation time of the
physical noise affects the mean dynamics of both the electric field amplitude
and the carrier number. We show that these are systematic corrections that can
be described by additional drift terms in the model.
