Effect of cross saturation on frequency fluctuations in a nearly single-mode semiconductor laser

The effect of side-mode cross-saturation on the frequency noise of the main mode of a nearly-single-mode laser is investigated by considering the Langevin rate equations which contain the nonlinear gain with both the self-saturation and cross-saturation terms. When cross-saturation is stronger than self-saturation, the frequency noise of the main mode is found to be significantly enhanced in the low-frequency regime (<1 GHz). An increase of more than 20 dB is predicted due to a side mode suppressed by 15-20 dB. The enhanced frequency noise results in broadening of the laser linewidth and may affect the performance of coherent optical communication systems.<
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