Effect of gain nonlinearities on period doubling and chaos in directly modulated semiconductor lasers.

The mode gain in semiconductor lasers decreases with an increase in power due to nonlinear processes such as spectral hole burning. When these small nonlinearities are included in the single- mode rate equations, it is found that they can eliminate the previously predicted sequence of period-doubling bifurcations leading to chaos in directly modulated semiconductor lasers. For InGaAsP lasers used in optical communication systems, the nonlinear effects are strong enough to rule out the possibility of chaotic behavior. The results also show that gain nonlinearities affect significantly the width and the shape of picosecond pulses generated by the method of gain switching.