Linewidth reduction of a 30mW-405nm GaN violet laser diode by optical-electrical double feedback method

We have demonstrated a compact and efficient frequency stabilization system based on Pound-Drever-Hall method, along with optical feedback. The frequency of a 30mW 405nm GaN violet laser diode (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-Hall technique. Moreover, by employing optical feedback from another tilted CFP cavity, the residual frequency noise has been efficiently suppressed. The minimum square root of the Allan variance was 1.65×10 at the integration time of 0.5s under the optical-electrical double feedback condition. We have achieved the stabilization of visible violet LD by optical feedback method for the first time.