On the prediction of the mode-partitioning floor in injection lasers with multiple side modes at 2 and 10 Gb/s

An analytical method is presented for estimating the error-rate floor to be expected in a digital transmission system using an injection laser. A computer model of the laser, including Langevin noise sources and with random sequences of signal pulses, is used to find the probability of the main-mode average power during an ON pulse being less than 0.5 times normal average power during an ON pulse event. With sufficient fiber dispersion, this constitutes a useful estimate of the mode-partitioning floor. Three methods are included for determining the floor: (1) direct calculation using a single Monte Carlo run; (2) extrapolation to floors in the 10^-10 region of a series of Monte Carlo runs for different laser modal loss differences (Δα); and (3) extrapolation of a single Monte Carlo run to low error-rate floors using a new analytical expression with parameters derived from the Monte Carlo run. In order to avoid a serious error-rate floor at 2 or 10 Gb/s, it is found that Δα must be about 10 or 30-35 cm^-1, respectively