Volume Reflection Gratings in Photorefractive Materials

Date of Award

12-1-2023

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Advisor: Partha Banerjee

Abstract

This dissertation is concerned with two distinct applications of volume gratings recorded in photorefractive electro-optic crystals. The first of two applications involves the use of these volume gratings to non-mechanically steer laser beams. A geometric and physical-optics based analysis shows the potential for writing programmable volume gratings in lithium niobate using visible wavelengths in the transmission geometry, and subsequently probing those gratings using infrared wavelengths in a reflection geometry. By appropriate adjustments made to the writing beams, it is shown that both the grating spacing and grating tilt angle can be controlled such that the grating becomes a rotatable Bragg mirror for the incident probe beam, thus steering it to desired angles. The second application of these volume gratings is in image processing. System transfer functions determining the spatial evolution of the reference (input wave) and signal (diffracted wave) beams as they propagate inside a self-pumped volume reflection grating are derived and solved numerically. The solutions are then used to highlight the spatial filtering properties of self-pumped volume reflection gratings, with the focus being on the transmitted (un-diffracted) portion of the reference beam, which is shown to be high-pass spatially filtered. The high-pass spatial filtering manifests as programmable 2-dimensional edge enhancement in the transmitted reference beam. Contrast analysis is done for edge enhanced images, both through simulations and experiments, which show a direct proportionality between the strength of edge enhancement seen in the filtered images and the intensity of the writing beam used to record the grating.

Keywords

volume gratings, volume reflection gratings, photorefractives, lithium niobate, beam steering, image processing, edge enhancement

Rights Statement

Copyright © 2023, author.

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