21 February 2007 Diffraction grating lens array
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Abstract
We have proposed a new type of camera module with a thin structure and distance-detection capability. This camera module has a four-lens-array with diffraction gratings (one for blue, one for red, and two for green). The diffraction gratings on the mold are formed mechanically, and the plastic lens array is fabricated by injection molding. The two green images are compared to detect parallax, and parallax-corrected blue, red and green images are then composed to generate a color image. We have developed new design software and molding technologies for the grating lenses. The depth and period of blazed gratings and the shapes of aspheric lenses are optimized; and blue, red and two green aspheric lenses with gratings are molded as a single four-lens-array. The diffraction gratings on both surfaces of each lens act to improve field curvature and realize wide-angle imaging. However, blazed gratings sometimes cause unnecessary diffraction lights that impede the formation ofhigh-resolution images. We have developed a new method to measure necessary first-order diffraction lights and unnecessary diffraction lights separately. Use of this method allows the relationship between molding conditions and necessary/unnecessary diffraction lights to be shown. Unnecessary diffraction lights can be diminished by employing the optimal molding processes, allowing our grating lenses to be used for image capture.
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Tsuguhiro Korenaga, Takamasa Ando, Seiji Moriguchi, Fuminori Takami, Yoshifumi Takasu, Seiji Nishiwaki, Masa-aki Suzuki, Michiyoshi Nagashima, "Diffraction grating lens array", Proc. SPIE 6501, Sensors, Cameras, and Systems for Scientific/Industrial Applications VIII, 65010T (21 February 2007); doi: 10.1117/12.702738; https://doi.org/10.1117/12.702738
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