Achievement of 1 MHz frequency stability of semiconductor lasers by double-loop AFC scheme

A temperature-controlling AFC system has been developed to realise high-frequency stability with semiconductor lasers. The frequency drift in DC operation can be reduced to below 1 MHz peak-to-peak. When necessary, the laser frequency can be modulated directly in the AFC state while the centre frequency is kept stabilised within 3 MHz. A heterodyne experiment was also performed using two frequency stabilised lasers; a stable IF output could be obtained for 10 min.