The frequency control of laser diodes

(Received 4 February 1991, accepted 6 April 1992)

Abstract
It is shown that spectral characteristics of laser diodes are rather poor and that frequency control methods are needed to be able to use laser diodes in numerous applications. We describe precisely the problems encountered with laser diodes and attempt to explain their origin. Various means used to control laser diodes frequency are then reviewed ; each of them can be used in order to obtain a better control on a particular feature needed for a given application. However, we put an emphasis on the Extended-Cavity laser solution which is shown to solve satisfactorily each problem. Another challenge consists in obtaining a good frequency control with high power laser diodes. We also describe the state of the art for this purpose and discuss the experiments already made.