Active Disturbance Rejection Control of Temperature for Ultrastable Optical Cavities

This paper describes the application of a novel active disturbance rejection control (ADRC) to the stabilization of the temperature of two ultra-stable Fabry–Pérot cavities. The cavities are 10 cm long and entirely made of ultra-low-expansion glass. The control is based on a linear extended state observer that estimates and compensates the disturbance in the system in real time. The resulting control is inherently robust and easy to tune. A digital implementation of ADRC gives a temperature instability of 200 μK at one day of integration time.