Operational states and intensity noise characteristics of time-delayed semiconductor lasers subject to strong optical feedback

Abstract

This article investigates the effects of strong optical feedback on the operational states and relative intensity noise fluctuations of long external cavity semiconductor lasers. Using modified rate equations, the findings show that the pulsation amplitude increases significantly, and the time to reach steady-state operation decreases when noise sources are included. Under strong optical feedback, the laser exhibits pulsating behavior, with relative intensity noise reduced to quantum noise level at high injection currents. In chaotic conditions, two peaks appear at the external and relaxation frequencies, indicating instability due to two threshold conditions related to the laser and external cavity. Consequently, the low-frequency relative intensity noise is elevated above quantum noise levels. Increasing the optical feedback and enhancing the injection current are essential for stable, low-noise pulsating laser operation.