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Proceedings Paper

Experiments in adaptive optical jitter control
Author(s): Mark A. McEver; Daniel G. Cole; Robert L. Clark
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Paper Abstract

Optical jitter, the centroid-shifting of a light image, concerns engineers and scientists working with lasers and electro-optical systems. Even micron-level relative motion between individual optical components such as mirrors and lenses causes optical jitter, resulting in pointing inaccuracy, blurred high-resolution images, and poor nanotechnology quality. Typical jitter control technology uses fast-steering mirrors to correct for structural and acoustic disturbances in the beam train. Unknown or time-varying disturbance characteristics necessitate a controller that can adapt its parameters in realtime. The application of one such adaptive feedback controller algorithm has been proposed by the authors. The algorithm uses a technique known as Q-parameterization to structure the controller as a function of plant coprime factors and a free parameter, Q. An inherent property of this structure is the formation of a disturbance estimate based on subtraction of the controller influence from the feedback signal. The free parameter, Q, filters this estimate to form a portion of the control signal. If the controller influence on the feedback signal is estimated from accurately modeled plant dynamics, the disturbance estimate contains no feedback information allowing Q to be designed in an open-loop fashion. A gradient descent Least Mean Squares (LMS) algorithm updates the coefficients of the filter Q in realtime to minimize the frequency-weighted RMS jitter. Experiments on an optical jitter control testbed with Q set to a 200-tap digital finite impulse response (FIR) filter resulted in jitter reductions of 35% - 50%, without requiring prior knowledge of the disturbance spectrum.

Paper Details

Date Published: 1 August 2003
PDF: 8 pages
Proc. SPIE 5049, Smart Structures and Materials 2003: Modeling, Signal Processing, and Control, (1 August 2003); doi: 10.1117/12.484057
Show Author Affiliations
Mark A. McEver, Duke Univ. (United States)
Daniel G. Cole, Duke Univ. (United States)
Robert L. Clark, Duke Univ. (United States)

Published in SPIE Proceedings Vol. 5049:
Smart Structures and Materials 2003: Modeling, Signal Processing, and Control
Ralph C. Smith, Editor(s)

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