Low-height camera modules are demanded for such applications as cellular phones and vehicles. For designing optical
lens, it has widely been recognized that a trade-off exists between reducing the number of lenses and camera resolution.
The optical performance of imaging lenses has been improved by diffraction gratings, which have a peculiar inverse
dispersion in the wavelength and exhibit the efficacy of correction for chromatic aberration. We can simultaneously
reduce the number of lenses and maintain optical resolution using diffraction gratings.
However, we have found a generation of striped flare lights under intense light sources that differ from unnecessary
order diffraction lights. In this paper, we reveal the generation mechanism of these new striped diffraction lights and
suggest a novel structure of diffraction gratings that can decrease them.
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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