Phase noise characteristics of single mode semiconductor lasers with optical feedback

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Abstract
The phase noise characteristics of single mode semiconductor lasers with optical feedback have been studied. A correlation is found between the suppression of the low-frequency noise and the enhancement of the high-frequency noise near the relaxation oscillation frequency. Contrary to previous analyses, the low-frequency noise is minimized when the reflected light is 70°–90° out of phase with respect to that inside the diode laser cavity. A calculation of the laser frequency fluctuation spectrum, taking into account the amplitude-phase coupling of the laser field, agrees with the observation. A new explanation is proposed for the feedback-induced phase noise reduction effect.