Enhanced intensity fluctuations in a laser diode subject to optical feedback

Abstract

The effects of optical feedback in edge-emitting semiconductor lasers and vertical cavity surface emitting lasers (VCSELs) have attracted considerable attention because the characteristics of both kind of lasers are very sensitive to the effects of reflected light. The phenomena arising in laser diodes subject to optical feedback can be classified according to operating five regimes conventionally identified as regimes I-V. Optical feedback also affects the noise properties of semiconductor lasers. There have been a number of investigations of the noise properties of semiconductor lasers and VCSELs subject to optical feedback. However, such work has been concerned with only some of the above-mentioned regimes of operation. A thorough experimental investigation of the effect of optical feedback in RIN of edge-emitting semiconductor lasers has yet to appear in the literature. In this paper, we present a detailed study of the effect of optical feedback on the average RIN of edge-emitting semiconductor lasers at different bias currents. An experimental study has been performed of the relative intensity noise (RIN) of a semiconductor laser in optical feedback regimes I to V. At low bias current, a low RIN is observed with low feedback feedback ratio, the RIN increased in the coherence collapse regime, then decreased again in regime V. The RIN in regime V is lower than that of the solitary laser. It is observed experimentally that an increase of the RIN occurs for intermediate levels of feedback. Such an increase in RIN appears to be related to enhanced intensity fluctuations. We will consider theoretical approaches to explaining the observed RIN characteristics.