Silicon Fresnel lens fabricated using greyscale lithography

Cheng-Po Chen; Jason Karp; Tim Toepfer; Oliver Boomhower; Jim Kretchmer; Shubhodeep Goswami; Sachin Dekate; Loucas Tsakalakos

doi:10.1117/12.2530649

30 August 2019 Silicon Fresnel lens fabricated using greyscale lithography

Cheng-Po Chen, Jason Karp, Tim Toepfer, Oliver Boomhower, Jim Kretchmer, Shubhodeep Goswami, Sachin Dekate, Loucas Tsakalakos

Author Affiliations +

Proceedings Volume 11104, Current Developments in Lens Design and Optical Engineering XX; 111040G (2019) https://doi.org/10.1117/12.2530649
Event: SPIE Optical Engineering + Applications, 2019, San Diego, California, United States

Abstract

A silicon Fresnel lens was designed and fabricated using a greyscale lithography technique to shape optical emissions from an edge-emitting semiconductor diode laser. The laser beam was collimated in the fast axis and allowed a ±3° divergence in the slow axis along with bias angle accomplished through lens decentering. The lens had an aperture of 6.8 mm × 2.2 mm and 1 mm in total thickness. The lens was first designed as a contiguous surface using conventional raytracing methods, and then converted to a Fresnel sag model with an etch depth of 6.25 micrometers. The sag model along with the manufacturing tolerances were fed back through numerical tools to refine the design and modify the lens shape and laser position. Optical profilometry of fabricated lens element found deviations from design and nonuniformity across the entire aperture, with over-etching in the center and under-etching toward the edge of the lens. Characterization of the fabricated lenses showed less than 5% deviation in etch depth. Collimation performance was measured to be less than 2 milliradians, which was in close agreement with design models. Greyscale fabrication of the lens element enabled complex curvatures to be combined and provided a compact solution for direct, single optic coupling of diode laser to free-space projection.

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Cheng-Po Chen, Jason Karp, Tim Toepfer, Oliver Boomhower, Jim Kretchmer, Shubhodeep Goswami, Sachin Dekate, and Loucas Tsakalakos "Silicon Fresnel lens fabricated using greyscale lithography", Proc. SPIE 11104, Current Developments in Lens Design and Optical Engineering XX, 111040G (30 August 2019); https://doi.org/10.1117/12.2530649

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KEYWORDS

Etching

Collimation

Silicon

Semiconductor lasers

Lens design

Grayscale lithography

Fresnel lenses

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