Frequency Locking of an Optical Cavity using LQG Integral Control

This paper considers the application of LQG integral control theory to a problem of cavity locking in quantum optics. The cavity locking problem involves controlling the error between the laser frequency and the cavity frequency. A model for the cavity system, which comprises of a piezo-electric actuator and an optical cavity is determined in the frequency domain using a subspace identification method. An LQG controller which includes integral action is synthesized to stabilize the frequency of the cavity at the laser frequency and to reject low frequency noise inherent in laser systems. The controller is discretized and is successfully tested in the laboratory after being implemented on a dSpace DSP board.