Digital locking of a three-mirror ring cavity

This paper presents results for digitally locking an experimental optical cavity. Locking an optical cavity refers to the process of matching the resonant frequency of the cavity with the input laser frequency in order to facilitate maximum energy build-up inside the cavity. The cavity used in this paper is a three-mirror ring cavity with a piezo actuator mounted on one of the mirrors, which is digitally controlled to hold the cavity in lock. An integral LQG controller is designed and digitally implemented in order to achieve cavity lock and the closed-loop step response is presented. This is compared with the closed-loop step response using a digital proportional-integral controller for the three-mirror cavity.