Frequency control of semiconductor lasers

The requirement of a stable single-wavelength coherent source [1] for high-speed, long-distance optical-fiber communication systems has imposed severe conditions on the frequency control of semiconductor lasers. The two main candidates for a dynamic single-wavelength source are (1) the DFB and DBR lasers and (2) the interference lasers. In this paper, we first review the performances of interference lasers of the internal-reflection type. Then, we compare the outstanding features and problems of the Bragg lasers and the interference lasers of both internal- and external reflection types. Finally, we propose a new laser structure, called the interference-DFB laser, to take advantage of the interference and DFB lasers. An analysis of this laser also provides valuable insights in understanding the behavior of the DFB laser.