Abstract

A solitary semiconductor laser has an intrinsic linewidth of ~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.¹ 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, we 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.

© 1985 Optical Society of America