Electrical Feedback For Attaining Ultrahigh Coherence In Semiconductor Lasers

Abstract

Electrical negative feedback was proposed to carry out simultaneously the four subjects in order to attain ultrahigh coherence in semiconductor lasers.Their experimental results were presented. They were: (1) Linewidth of field spectrum was reduced to 200 kHz, which was narrower than the value given by the Schawlow-Townes' formula, i. e., the one limited by spontaneous emission.(2) Fluctuations of center frequency of field spectrum were reduced to 500 Hz at the integration time of 100 s. (3) Frequency tracking of the slave laser to the master laser was carried out with the frequency stability as high as that of the master laser given (2). (4) Wideband frequency tuning of the slave laser was carried out under the condition of (3). The resultant lock range was 47.3 GHz, in which the stability of the slave laser was maintained as high as that of (3).