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UBC Theses and Dissertations

Electro-optic diffraction grating employing electrophoresis, supercapacitance, and total internal reflection Radel, Jason C.


Light beam steering is required in fields ranging from industrial laser drilling to telecommunications. Current methods for light beam steering to angles greater than 10° rely on mechanically moving parts, which results in expensive and difficult-to-maintain systems. An alternative method for light beam steering is presented that redirects a light beam to an angle of 33° without the need for moving parts. This is achieved by altering the reflectance of a surface by controlling the concentration of dye ions in a region adjacent to an optically transparent and electrically conductive thin film. Non-mechanical light deflection is achieved by altering the reflectance of a diffraction grating (an electro-optic method), an approach that creates new diffraction peaks that lie between those associated with the original grating spacing. This method for electro-optic diffraction is made practical by the supercapacitance exhibited at the interface between a layer of indium tin oxide (ITO) and a solution consisting of methylene blue dye ions dissolved in water. This interface was examined and measured to have a capacitance of 40 F/m² with a corresponding reversible change in the reflectance of this interface of greater than 50%. The capability of this method to reversibly deflect light was experimentally verified by fabricating test cells consisting of two glass plates, each coated with a thin film of ITO. A solution of methylene blue dye ions dissolved in water was sealed between the two plates. Electro-optic diffraction modulation was demonstrated by patterning one of the two ITO films into an interdigitated design, done via standard photolithography techniques for initial experimental verification, and via focused ion beam milling for sub-micron scale electrodes. An electrical potential difference was applied between the interdigitated ITO electrodes and the radiant flux of the newly created diffraction peaks was measured. The light distribution that reflected by means of total internal reflection from the ITO/solution interface was measured to reversibly shift 0.7% of the incident light to new diffraction peaks. This approach may be useful in applications where large diffractive deflection angles are required and alternate beam-steering methods are impractical.

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