Laser beam pointing and stabilization by intensity feedback control

This paper presents an investigation of the control problem of aiming a laser beam under dynamic disturbances, using light intensity for feedback. The beam is steered with a bi-axial MEMS mirror, which is driven by a control signal generated by processing the beam intensity sensed by a single photodiode. Since the pointing location of the beam is assumed to be not available for real-time control, a static nonlinear mapping from the two-dimensional beam location to the sensor measurement is estimated with the use of the least-squares algorithm, using data from an optical position sensor (OPS). The previous formulation results in a state-space system model with a nonlinear output function. The controller design problem is addressed with the integration of an extended Kalman filter (EKF) and a pair of linear time-invariant (LTI) single-input/single-output (SISO) controllers into one system. In order to demonstrate the effectiveness of the proposed approach, experimental results of a case relevant to free-space optics for communications and directed energy applications is presented here.