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Theses and Dissertations

2008

Optics

Articles 1 - 8 of 8

Full-Text Articles in Physical Sciences and Mathematics

Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema Sep 2008

Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema

Theses and Dissertations

A self-referencing interferometer based closed-loop adaptive optics controller is developed which is designed to operate effectively under strong turbulence conditions. The aberrated optical field is modeled stochastically and then estimates of the state of the system are developed using a steady-state, fixed-gain Kalman filter. The phase of the optical field is considered the state of the system which is wrapped in a limited range of (-π, π]. This phase is unwrapped through the use of a least-squares reconstructor which has been modified to work effectively in the presence of branch points associated with strong turbulence. The conjugate of the optical …

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Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey Aug 2008

Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey

Theses and Dissertations

The objective of this research effort was to demonstrate the path to continuous wave, coherent beam combination through stimulated Brillouin scattering phase conjugation in optical fiber. This work experimentally determined the fiber parameters necessary for phase conjugation in step-index optical fiber. Continuous wave phase conjugation using stimulated Brillouin scattering in step-index fibers was achieved for the first time with a fidelity of 0.8 and a threshold power of 16 W in a 15-m fiber with 0.13 NA. A fidelity of 0.8 was also achieved using 40 m of fiber with 0.06-NA and a threshold power of 15 W. The fidelity …

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Analysis Of Non-Uniform Gain For Control Of A Deformable Mirror In An Adaptive-Optics System, Kevin P. Vitayaudom Mar 2008

Analysis Of Non-Uniform Gain For Control Of A Deformable Mirror In An Adaptive-Optics System, Kevin P. Vitayaudom

Theses and Dissertations

The Air Force Research Laboratory’s Sodium Guidestar Adaptive Optics for Space Situational Awareness program (NGAS) has sponsored research on spatially non-uniform gain for the servo-loop controller of an adaptive optics (AO) system. The edge subapertures of a Shack-Hartmann wavefront sensor have lower signal-to-noise ratios and are more susceptible to measurement errors than fully illuminated center subapertures. These measurement errors produce errant commands over the corresponding edge actuators and can induce instabilities over these regions in strong turbulence conditions. The objective of this research was to develop and experimentally verify the use of spatially varying gain maps on the servo-loop controller …

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Tightly Integrating Optical And Inertial Sensors For Navigation Using The Ukf, Sedat Ebcin Mar 2008

Tightly Integrating Optical And Inertial Sensors For Navigation Using The Ukf, Sedat Ebcin

Theses and Dissertations

The motivation of this research is to address the benefits of tightly integrating optical and inertial sensors where GNSS signals are not available. The research begins with describing the navigation problem. Then, error and measurement models are presented. Given a set of features, a feature detection and projection algorithm is developed which utilizes inertial measurements to predict vectors in the feature space between images. The unscented Kalman filter is applied to the navigation system using the inertial measurements and feature matches to estimate the navigation trajectory. Finally, the image-aided navigation algorithm is tested using a simulation and an experiment. As …

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Modeling Of Sbs Phase Conjugation In Multimode Step Index Fibers, Justin B. Spring Mar 2008

Modeling Of Sbs Phase Conjugation In Multimode Step Index Fibers, Justin B. Spring

Theses and Dissertations

Stimulated Brillouin scattering in a multimode step-index fiber can be used to generate a counter-propagating, phase-conjugate beam that would prove useful in many applications, such as near diffraction limited, double-pass high-power amplifiers or coherent beam combination. Relatively little modeling of such a fiber-based phase conjugator has been done, making design decisions regarding type and length of fiber largely guesswork. A numerical model was constructed with the aim of providing educated predictions about the phase conjugate fidelity that could be expected from a given pump intensity input coupled into a specific fiber. A numerical perturbation algorithm was constructed to search for …

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Collision Avoidance For Uavs Using Optic Flow Measurement With Line Of Sight Rate Equalization And Looming, Paul J. Shelnutt Mar 2008

Collision Avoidance For Uavs Using Optic Flow Measurement With Line Of Sight Rate Equalization And Looming, Paul J. Shelnutt

Theses and Dissertations

A series of simplified scenarios is investigated whereby an optical flow balancing guidance law is used to avoid obstacles by steering an air vehicle between fixed objects/obstacles. These obstacles are registered as specific points that can be representative of features in a scene. The obstacles appear in the field of view of a single forward looking camera. First a 2-D analysis is presented where the rate of the line of sight from the vehicle to each of the obstacles to be avoided is measured. The analysis proceeds by initially using no field of view (FOV) limitations, then applying FOV restrictions, …

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Nonmechanical Multizoom Telescope Design Using A Liquid Crystal Spatial Light Modulator And Focus-Correction Algorithm, Eric W. Thompson Mar 2008

Nonmechanical Multizoom Telescope Design Using A Liquid Crystal Spatial Light Modulator And Focus-Correction Algorithm, Eric W. Thompson

Theses and Dissertations

Theoretical development and design of a compact nonmechanical multi-zoom telescope system is presented. A liquid crystal spatial light modulator (LC SLM) enables selection of four separate beam paths without the use of moving parts. Each path incurs a different focus aberration in the image plane that can be deconvolved with postprocessing to yield four possible corrected magnification options. To increase flexibility, each region has a 40-wave subrange of focus. Optical zooms of up to 10 times magnification are feasible and are limited only by system noise and signal to noise ratio. Elimination of moving parts for focus could prove beneficial …

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Limitations Of Segmented Wavefront Control Devices In Emulating Optical Turbulence, Michael D. Plourde Mar 2008

Limitations Of Segmented Wavefront Control Devices In Emulating Optical Turbulence, Michael D. Plourde

Theses and Dissertations

Using a device to act as a surrogate for atmospheric turbulence in a laboratory is necessary to build and test optical systems for imaging, lidar, laser weapons, and laser communications. Liquid-crystal spatial light modulators (LC SLMs) and segmented micro-electro-mechanical-system (MEMS) deformable mirrors (DMs) are commonly used devices for altering wavefronts in order to simulate a portion of atmospheric turbulence. The best location of these devices was theoretically analyzed to obtain the broadest possible range of atmospheric conditions. It was found that two phase screens should be placed at the beginning of the optical path to achieve maximum turbulence strength for …

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