ON THE PREDICTION OF THE MODE-PARTITIONING FLOOR IN INJECTION-LASERS WITH MULTIPLE SIDE MODES AT 2 AND 10 GB/S

A new 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. It is also found that single-mode lasers, biased near threshold and using pulse rates near 10 Gb/s, will exhibit an error-rate floor in fiber transmissions systems due to failure of the laser’s total power to rise above 0.5 times the normal average power; lower pulse rates or bias above threshold eliminates these errors. © 1990 IEEE