Correlation between intensity noise and longitudinal modes of a semiconductor laser coupled to an external cavity

Abstract

Correlation between intensity noise and fine structures of longitudinal modes in a semiconductor laser coupled to an external cavity has been investigated. It is experimentally shown that the intensity noise is perfectly suppressed when the laser oscillates in ‘‘pure’’ single frequency oscillation even with strong optical feedback. Intensity noise, which arises only when several external cavity modes exist, is interpreted in terms of the time-dependent refractive index in the semiconductor cavity caused by the light beatings among the lasing modes.