MODELING MODE PARTITION NOISE IN NEARLY SINGLE-MODE INTENSITY MODULATED LASERS

A new theoretical model of mode partitioning in an intensity modulated nearly single-mode semiconductor laser biased near threshold is described. A kev feature of the model is the use of an artificial absorbing barrier that enables us to separately treat the initial stochastic turn-on of the modes and their subsequent deterministic evolution. For the stochastic turn-on, two regimes of behavior have been identified which are distinguished by the degree of correlation between the fluctuations of the main and side modes. The turn-on statistics for both regimes are separately derived from the solution of an approximate Fokker-Planck equation. Expressions are given for the probability density functions of the averaged power in the modes during a data ''1'' pulse. In particular, for low probabilities, the probability density function of the averaged side mode power is exponential with a decay rate proportional to the product of the bit period and gain difference between the modes. Probability density functions derived from the model and from Monte Carlo simulations show excellent agreement over a large range of probabilities.