Precision glass molding (PGM) of chalcogenide lenses has become an enabling technology for high volume thermal imaging applications. The molding machines that facilitate this technology vary widely in design, functionality, and cost. The machines range from single-axis compact machines and large-scale fixed die machines to progressive transfer molding machines and highly customized systems for specialized applications such as wafer level molding. These technologies are compared and contrasted with specific attention paid to the intricacies of precision molding of chalcogenide glass.
We report our progress on the design, modeling, and fabrication of a step-index miniature spherical retroreflector for use
in the mid- and long-wave infrared region (3 μm-12 μm). Efficient retroreflectors with large acceptance angles and
isotropic performance have several defense applications - for instance, target tracking and monostatic LIDAR. The ideal
isotropic spherical retroreflector is epitomized by the spherical Luneburg lens, which brings a collimated beam to a
perfect focus on the rear surface of the sphere due to its gradient index profile and spherical symmetry. The ideal
Luneburg lens' gradient profile, however, must have an index value equal to that of the immersion medium at its
boundaries; therefore, rendering its fabrication infeasible for applications in air. Although spherical gradient index
designs can provide a good approximation of the Luneburg lens, as of now there have been no demonstrated methods of
fabricating such lenses, especially for mid- and long-wave infrared applications. Consequently, we have designed a
retroreflector with a step-index approximation to a spherical gradient index design with comparable optical performance
to the spherical gradient index ideal. This retroreflector design can be fabricated by molding a higher index chalcogenide
glass shell as a cladding layer over a lower index core such as ZnS using glass compression molding.
This paper presents the design, analysis, and fabrication of a telecentric f/1.3 thermal imaging lens. The 14.8 mm wideangle
lens provides a 62° diagonal field-of-view, and was designed to operate over the 8-14 μm infrared spectral band. Focus can be manually adjusted from 0.5 m to infinity, maintaining constant image quality over the entire range. A compact air-spaced doublet design limits the overall length to 34 mm and the maximum diameter to 28 mm. Lens materials were chosen to minimize chromatic aberrations, reduce cost, and fit within the molded chalcogenide glass
manufacturing capabilities. Combining a molded aspheric chalcogenide lens with a polished spherical Germanium lens eliminated the need for a diffractive surface to correct chromatic aberrations, and reduced the fabrication cost. Vignetting was purposely introduced at the extreme fields to compensate for the effects of aberrations on the relative illumination variation across the field-of-view. Athermalization of the lens was achieved mechanically over the entire operating temperature range (- 40 to + 80°C).
Conference Committee Involvement (1)
Polymer Optics and Molded Glass Optics: Design, Fabrication, and Materials 2022
22 August 2022 | San Diego, California, United States
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