Multi-aperture Phase-contrast Sensor for Complex Field Retrieval in Strong Scintillations

Date of Award

2018

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics

Advisor/Chair

Advisor: Mikhail Vorontsov

Abstract

As an optical beam propagates over near-horizontal paths the beam will be scattered, absorbed or distorted due to the motion and characteristics of atmospheric components. The main characteristic of the atmosphere that results in significant distortion to the propagating optical beam is atmospheric turbulence. Solar heating causes convective currents and random changes of the refractive index. In addition to the atmospheric turbulence, refractivity will change the beam's trajectory as it propagates through the atmosphere. Mirages are a well-known example of visible light refraction due to the atmosphere. In this study we will consider turbulence-induced negative effects on optical beam wavefront phase and introduce a novel sensor for optical field and/or wavefront phase reconstruction. Since the optical field amplitude, equivalent to the square root of intensity, is directly measurable, the wavefront phase is the most challenging to accurately measure as it must be indirectly reconstructed from one or more intensity measurements. Considerable efforts have been made to reconstruct the wavefront phaseand subsequently mitigate the wavefront phase error for applications such as adaptive optics (AO). However, the operational range of current wavefront sensors (WFSs) is limited to weak and moderate turbulence conditions. A multi-aperture complex field (MACF) sensor based on an array of densely packed Zernike-type phase contrast filters is introduced and analyzed using wave-optics numerical simulations. The MACF sensor doesn't require a coherent reference wave for complex field (wavefront phase and amplitude) reconstruction from the measurements that are performed using pupil and output-plane photo-arrays. It is shown in this study that for solely wavefront phase retrieval only a single output-plane photo-array can be utilized. Different MACF sensor optical configurations and phase retrieval algorithms are considered and optimized to improve computational efficiency and accuracy of high-resolution wavefront phase retrieval in the conditions of strong intensity fluctuations (scintillations) of the input field. These intensity scintillations result from optical wave propagation in a media with volume random refractive index variations (e.g. atmospheric turbulence), and/or scattering off an extended target with randomly rough surface. Finally, The MACF sensors applications in adaptive optics systems operating in strong intensity scintillation conditions are discussed.

Keywords

Engineering, Optics, Complex Field and Wavefront Sensing, Active or Adaptive Optics, Atmospheric Turbulence, Branch Points, Strong Intensity Scintillations, Zernike Filter

Rights Statement

Copyright © 2018, author

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