Importance

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Abstract

A method for fabricating gradient-index rods and rod arrays. A central rod of optical glass having predetermined properties and predetermined outside dimensions is placed inside a tube of optical glass having predetermined properties and predetermined outside dimensions, to form an assembly. The inside dimensions of the tube are substantially equal to the outside dimensions of the rod. The tube is formed of a plurality of coaxial sleeves, the outside dimensions of each interior sleeve being substantially equal to the inside dimensions of the next adjacent sleeve, each sleeve having a selected refractive index so that, together with the tube, the refractive indices from the central rod through the outermost sleeve approximate the refractive index profile of the gradient-index rod to be fabricated. The central rod and sleeve material is selected so that their respective thermal indices of expansion are substantially equal. The central rod and tube assembly is placed in a mold having inside dimensions substantially equal to the outside dimensions of the tube. The mold is oriented vertically so as to ensure that there is no net lateral gravitational force on the assembly. The mold is then heated with the central rod and the tube therein at a predetermined temperature for a predetermined time so as to cause a selected amount of diffusion of material between the central rod and the sleeves and thereby produce a radial refractive index gradient. The temperature is then gradually reduced to anneal the glass. The cooled glass comprises a preform which is then drawn into a gradient-index rod. Gradient-index elements fabricated in accordance with the invention may be placed into a substrate and drawn into elements that have a desired external shape while retaining the optical properties of a radially symmetric, cylindrical gradient-index rod. Arrays of gradient-index rods fabricated using the invention may also be bonded together or imbedded in a substrate.

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First Claim