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Abstract

Variable focus optical system in which a light beam is projected through a transparent flat cell of electro-optic material coated on both sides with a layer of transparent conductive material. The layer on one side of the cell is divided into a central disc region and a ring shaped region which surrounds the central region. A lens focuses the light transmitted through the cell at a predetermined distance from the lens. An AC voltage is applied between one of the regions and the layer on the opposite side of the cell to vary the phase of the light passing through that region and focus that portion of the light at a distance which varies periodically with the AC voltage. A reflective surface is positioned at the distance from the lens where the unshifted light is focused, and a detector receives the light reflected from the reflective surface and provides an output signal indicative of the position of the surface.

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First Claim