B.W. Frazier

Bio: B.W. Frazier is an academic researcher from University of North Carolina at Charlotte. The author has contributed to research in topics: Adaptive optics & Robust control. The author has an hindex of 1, co-authored 1 publications receiving 15 citations.

Robust control of an adaptive optics system

Abstract: Adaptive optics systems are concerned with the real-time correction of blurred images and have applications in astronomical imaging, freespace optical communications and high-energy laser beam guidance. This paper outlines the proposed design for an adaptive optics system that utilizes modern H/sub /spl infin// control theory to optimize the robustness of the system.

Feedforward Control of Deformable Membrane Mirrors for Adaptive Optics

Abstract: In this paper, performance enhancements for deformable membrane mirrors based on model-based feedforward control are presented. The investigated deformable mirror consists of a flexible membrane and voice coil actuators. Feedback control of the distributed actuators cannot be implemented in these mirrors due to a lack of high speed internal position measurements of the membrane's deformation. However, by using feedforward control, the dominant dynamics of the membrane can still be controlled allowing for faster settling times and reduced membrane vibrations. Experimental results are presented for an ALPAO deformable mirror with 88 distributed actuators on a circular membrane with a pupil of two centimeters in diameter.

Online constrained receding horizon control for astronomical adaptive optics

Abstract: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Publications and Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Modeling and Control of Deformable Membrane Mirrors

Abstract: The use of deformable mirrors (DMs) in adaptive optics (AO) systems allows for compensation of various external and internal optical disturbances during image aquisition. For example, an astronomical telescope equipped with a fast deformable secondary mirror can compensate for atmospheric disturbances and wind shake of the telescope structure resulting in higher image resolution [1–4]. In microscopy, deformable mirrors allow to correct for aberrations caused by local variations of the refractive index of observed specimen. Especially confocal and multi-photon microscopes particularly benefit from the improved resolution for visualization of cellular structures and subcellular processes [5, 6]. In addition, results of applied adaptive optics for detection of eye diseases and in vitro retinal imaging on the cellular level show promising examination and treatment opportunities [7–9].

Control of a deformable mirror subject to structural disturbance

Abstract: Future space based deployable telescopes will be subject to non-atmospheric disturbances. Jitter and optical misalignment on a spacecraft can be caused by mechanical noise of the spacecraft, and settling after maneuvers. The introduction of optical misalignment and jitter can reduce the performance of an optical system resulting in pointing error and contributing to higher order aberrations. Adaptive optics can be used to control jitter and higher order aberrations in an optical system. In this paper, wavefront control methods for the Naval Postgraduate School adaptive optics testbed are developed. The focus is on removing structural noise from the flexible optical surface using discrete time proportional integral control with second order filters. Experiments using the adaptive optics testbed successfully demonstrate wavefront control methods, including a combined iterative feedback and gradient control technique. This control technique results in a three time improvement in RMS wavefront error over the individual controllers correcting from a biased mirror position. Second order discrete time notch filters are also used to remove induced low frequency actuator and sensor noise at 2Hz. Additionally a 2 Hz structural disturbance is simulated on a Micromachined Membrane Deformable Mirror and removed using discrete time notch filters combined with an iterative closed loop feedback controller, showing a 36 time improvement in RMS wavefront error over the iterative closed loop feedback alone.