Optical frequency stabilisation and linewidth reduction of a multielectrode DFB laser with current feedback

Optical frequency stabilisation and linewidth reduction by the current feedback technique were studied with a multi-electrode DFB laser. In the current feedback technique, phase rotation in the feedback loop, particularly induced by a laser, is the fundamental problem. This problem was resolved by using multielectrode DFB lasers without phase inversion. We simultaneously succeeded in optical frequency stabilisation and linewidth reduction with only one feedback electrical circuit. Optical frequency drift and spectral linewidth were reduced to 1/14 and 1/126, respectively, of those in the free-running state. The minimum spectral linewidth obtained was 95 kHz.