Dynamical and coherent characteristics of semiconductor lasers with external optical feedback

The effects of the external feedback on the noise properties of semiconductor laser are studied based on the feedback- induced-dynamics. The steady-state analysis shows that the oscillation mode can be determined from the phase condition in the way that the mode with the maximum stability factor is selected rather than the mode with the minimum excess gain. Both the phase and intensity noises are investigated by including Langevin noise sources in the rate equations. As the feedback level increases, the linewidth and the relative intensity noise level exhibit three different stages of variations leading to coherence collapse state where the corresponding dynamics is fully chaotic. A double- external-cavity model is proposed as an example to stabilize the feedback-induced chaos. Numerical results indicate that, for certain parameter range, the original chaos can be stabilized to periodic oscillations or fixed states and consequently, the linewidth and the RIN level in the low- frequency range can be reduced to the extent of the solitary laser.