OPTICAL FEEDBACK PHASE-AUTOLOCKING OF A SEMICONDUCTOR LASER.

A solitary semiconductor laser has an intrinsic linewidth of similar 15 MHz at 5 mW. A reduction in this broad linewidth is necessary for coherent applications. It has been demonstrated recently that a reduction of the laser linewidth by as much as a factor of 100 can be achieved by using a low-level optical feedback. However, this rather simple method of reducing the linewidth suffers from the problem that the degree of linewidth narrowing depends on the phase of the optical feedback. In addition, mode-hopping can occur which also depends on the phase and the amount of feedback. In this paper, the authors present a method to control the phase of the optical feedback so as to maintain a stable laser operation at a particular feedback level with the minimum linewidth.