Linewidth reduction of a 30m W 657nm visible laser diode by optical-electrical double feedback method

摘要

We have stabilized frequency of 35mW 680nm visible laser diode (LD) by using simple frequency stabilization system based on optical-electrical double feedback method. For the long-term frequency stabilization, frequency of the LD was stabilized to a reference confocal Fabry-Perot cavity (CFP cavity) by negative electrical feedback to the injection current of the LD based on Pound-Drever technique. By employing optical feedback from another tilted CFP cavity along with electrical feedback, the residual frequency noise has been efficiently suppressed The achieved PSD of frequency fluctuation under optical-electrical double feedback condition was less than 1 X 10~5 [Hz~2/ Hz] within the Fourier frequency < 10 MHz. The reduced linewidth under the double feedback condition is estimated to be narrower than at least 400 kHz, which seems to be the resolution limit of our measurement. The minimum square root of the Allan variance is 3.9x10~(-11) at the integration time of 0.1 msec under the double feedback condition.