Noise suppression of relaxation oscillation intensity in a microcavity Raman laser

Microcavity lasers have received widespread attention because of their miniaturization and low threshold characteristics. Based on the theoretical analysis of modified semiclassical Langevin equations and the dynamic response of a microcavity Raman laser under constant injection of external feedback light, optical feedback technology is proposed as an effective method for suppressing the relaxation oscillation noise of microcavity lasers. By controlling the optical feedback level, an overall suppression on the laser intensity spectrum around the relaxation oscillation frequency by approximately 24 dB is implemented experimentally. The phase portrait merging feature and the relaxation linewidth narrowing of the microcavity laser is also observed. The theoretical predictions, confirmed by numerical resolutions, are in good agreement with the experimental results. To the best of our knowledge, this work is the first to study the optical feedback effect in the miniaturized microcavity lasers. The all-optical technique offers a simple and effective method for relaxation oscillation noise reduction in microcavity lasers without active control system. From the applied point of view, since the relaxation oscillation, and consequently the intensity noise of the microcavity laser can be modified by applying the optical feedback, it opens up new perspectives for ultrasensitive detection in a low noise microcavity-based laser system.