Design, fabrication, and metrology of polymer gradient-index lenses for high-performance eyepieces

Abstract

High-performance eyepiece designs have been carried out using both spherical and radial gradient-index (GRIN) elements. Eyepiece designs of both geometries are shown to offer superior imaging performance with fewer elements when compared to purely homogeneous systems. These GRIN lenses are formed from monomer diffusion between polymethyl methacrylate (PMMA) and polystyrene (PSTY) during the polymerization process, resulting in a copolymer of the two homogeneous materials. A process for fabricating spherical GRIN elements is discussed where copolymer axial GRIN blanks are thermally compressed using spherical surface molds. This process curves the nominally-straight isoindicial surfaces of the axial GRIN rod to be consistent with the shape found during optimization of the design. Once compressed, the spherical blanks are diamond-turned for final surface figure and finish. Measurement of the GRIN profile is carried out using the Schmidt immersion technique in a Mach-Zehnder interferometer. Tolerances specific to GRIN elements are identified and determined to be readily achievable using the aforementioned manufacturing process.