The adaptive control of optical beam jitter

Abstract

Acquisition, Tracking and Pointing (ATP) of space and airborne optical beams is becoming an important research topic as the requirements for the control of the beam is increasing. Arc-second accuracy and nano-radian jitter coupled with stringent pointing requirements test the limits of control systems. A unique Laser Jitter Control Testbed was built in order to study means to correct disturbances in a laser relay system. A new technique, the Adaptive Bias Filter (ABF), applies a compensating bias to the reference signal for the adaptive filter, allowing rapid convergence in correcting narrowband disturbances. A second technique, the Adaptive Delay Filter (ADF), was applied in a new way to the adaptive control systems to better correlate the error signal with the reference signal. Experiments using these techniques effectively demonstrated the usefulness of the new control methods, including the use of a combination Linear Quadratic Regulator (LQR) and LMS/ABF filter to remove disturbances caused by colored noise injected into an optical beam. The combination controller results in a 38 dB decrease in jitter caused by a 50 Hz vibration and a 10 dB decrease in an 87 Hz vibration of the supporting platform, and an overall 75% improvement in the broadband jitter experienced by the optical beam.