Closed-loop laser noise suppression with a variable optical attenuator for fiber-integrated diamond quantum sensor

Abstract We present a miniaturized diamond quantum sensor integrated with a real-time laser noise suppression module, ensuring reliable operation for high-precision magnetic field measurements in the long-run. A piezoelectric micro-electromechanical systems mirror based variable optical attenuator (VOA) is constructed with an attenuation range of −3 dB to −20 dB. The VOA is employed to dynamically adjusts the intensity of reference laser signal to actively track diamond fluorescence signal and the laser noise is suppressed, whereby a sensitivity of 211 pT·Hz −1/2 is achieved. For real-time fluorescence tracking, a closed-loop control system is implemented to maintain functional common-mode rejection (CMR). Compared with passive CMR configuration (open-loop), the dynamic magnetic field noise of the closed-loop diamond sensor is reduced by 1.6 times in both challenging scenarios, including laser power fluctuations and strong magnetic fields. Furthermore, an optimal sensitivity is effectively maintained in a 2 h measurement time. Compared with open-loop operation, the sensitivity fluctuation of the closed-loop system is reduced by a factor of 14.29. The fluorescence tracking scheme provides an effective approach to enhancing the operational stability for practical magnetic sensing applications.