Binary optics thin-film microlens array

M. Edward Motamedi; Robert J. Anderson; R. de la Rosa; Leonard G. Hale; William J. Gunning III; Randolph L. Hall; Mohsen Khoshnevisan

doi:10.1117/12.138890

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13 January 1993 Binary optics thin-film microlens array

M. Edward Motamedi, Robert J. Anderson, R. de la Rosa, Leonard G. Hale, William J. Gunning III, Randolph L. Hall, Mohsen Khoshnevisan

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Proceedings Volume 1751, Miniature and Micro-Optics: Fabrication and System Applications II; (1993) https://doi.org/10.1117/12.138890
Event: San Diego '92, 1992, San Diego, CA, United States

Abstract

Binary optics can produce microlenses and lens arrays with theoretical diffraction efficiency as high as 95% for eight-phase level devices. Due to shadowing, mask misalignment, and etching errors that accumulate during fabrication, the actual diffraction efficiency can be reduced to less than 70%. Advances in mask design and e-beam writing have reduced mask misalignment errors to less than 0.2 micrometers but the major issue is the accuracy of the RIE process that is used to transfer a lithographic pattern into the substrate. RIE has two limitations for binary optic applications. First, it cannot be readily employed for the wide range of possible optical substrates of interest (Al₂O₃ for example), and second, since the pattern is etched directly into the substrate, there is no simple means to calibrate the etch depth during the process. Thin film deposition of the binary structure addresses both of these limitations. It is applicable to a wide range of materials, and accurate in process monitoring of the deposit permits precise control of the feature height. In this paper, we report on eight-phase level binary optic microlenses processed by deposition of SiO₂ on fused silica and Al₂O₃ on sapphire using a projection lithography system. Photoresist processing was achieved by image reversal and lift-off technique. The microlens arrays (in a square format) were designed for (lambda) equals 0.632 micrometers with two microlens sizes of 120 micrometers X 120 micrometers and 240 micrometers X 240 micrometers having speeds of F/12 and F/6 (at the corners), respectively. Optical characterization has demonstrated that the microlens arrays are near diffraction limited and diffraction efficiency is in excess of 80%.

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M. Edward Motamedi, Robert J. Anderson, R. de la Rosa, Leonard G. Hale, William J. Gunning III, Randolph L. Hall, and Mohsen Khoshnevisan "Binary optics thin-film microlens array", Proc. SPIE 1751, Miniature and Micro-Optics: Fabrication and System Applications II, (13 January 1993); https://doi.org/10.1117/12.138890

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