Generation of equidistant frequencies in a semiconductor laser with an external cavity

A cw semiconductor laser with external feedback provided by a diffraction grating was investigated experimentally. The laser drive current was modulated at a frequency of 0.3 — 5 GHz. The spectrum of the output radiation consisted of several equidistant frequencies and the intervals between these frequencies were determined by the current-modulation frequency. Optimal conditions were found for the generation of the maximum number of such frequency components. The maximum width of the spectrum was 48 GHz. A method was developed for measuring the difference frequencies in the optical range with the aid of such lasers.