Effect of fiber-far-end reflections on intensity and phase noise in InGaAsP semiconductor lasers

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Abstract
The effect of optical feedback on the intensity-noise spectrum and the longitudinal-mode line shape of a 1.55-μm InGaAsP laser is investigated for reflections arising from the far end of a 7.5-km-long fiber. The intensity noise near the relaxation-oscillation frequency is significantly enhanced by the reflection feedback. Owing to the intercavity coupling, the enhancement is, however, frequency dependent and the noise spectrum exhibits high-contrast modulations with a period corresponding to the fiber-cavity longitudinal-mode separation. A simple rate equation model is used to explain the observed behavior.