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

The effect of optical feedback on the intensity-noise spectrum and the longitudinal-mode line shape of a 1.55micron 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 inter-cavity coupling, the enhancement is however frequency dependent and the noise spectrum exhibits high-contrast modulation with a period corresponding to the fiber-cavity longitudinal-mode separation.