Date of Award

2-24-2009

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering

Department

Department of Electrical and Computer Engineering

First Advisor

Gregory J. Toussaint, PhD

Abstract

Adaptive optics applies advanced sensing and control to improve the ability of optical systems to collect images through a turbulent atmosphere. The results of this research effort demonstrate that the combination of two recent approaches improves the performance of adaptive optics in directed energy and laser communication scenarios. The first approach is adaptive control, which offers improved performance over fixed-gain controllers in the presence of rapidly changing turbulence. The second approach incorporated into the study is a dual-mirror system. The two mirrors are a high-bandwidth, low-actuator-stroke (tweeter) mirror and a low-bandwidth, large actuator-stroke (woofer) mirror. The woofer-tweeter combination allows for better compensation of the large-variance, high-spatial-frequency phase distortion generated by strong turbulence. Two different adaptive controllers are presented, one using a relatively simple model reference adaptive system controller and one using a lattice filter controller. The lattice filter is implemented in two ways. In one implementation the filter operates on the individual actuators, while in the other it operates on frequency weighted modes. The modal implementation reduces the computational burden of the filter. The performance of the different adaptive controllers is compared to both each other and to a traditional fixed-gain controller. Simulations show that adaptive control of woofer-tweeter AO can increase the mean Strehl ratio by up to 20%. In general, the lattice filter controllers outperform the model reference adaptive system controller. However, in cases where the lattice filter cannot use a sufficient number of modes, the model reference adaptive system can outperform the lattice filter.

AFIT Designator

AFIT-GE-ENG-09-33

DTIC Accession Number

ADA498818

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