Apposition compound-eye glass-plate optics with four-pixel imaging units for a 600  dpi high-resolution color image scanner

We propose an image scanner capable of capturing high-resolution images of closely positioned objects using a microlens array, where each microlens captures images of four pixels without gaps. Typically, an apposition compound-eye has only one photodetector per ommatidium, making high-resolution imaging challenging. We developed glass plate optics by arranging 1769 microlenses in a staggered two-row configuration on the surface, enabling the capturing of color images with a high-resolution of 600 dpi and a long reading width of 300 mm. The primary advantage of this compound-eye optical system is its thin profile, with a total thickness of only 7.4 mm, including its housing. It has a working distance of 6 mm and a large depth of field of 6 mm (with a modulation transfer function of over 30% at 5.7 line-pairs (lp)/mm). This allows for clear imaging of objects with surface irregularities, which is difficult with conventional contact image sensors. Our glass plate optics is constructed by bonding two glass plates: one with a microlens array molded on its surface and another serving as a light shield and apertures. Key optical design considerations include making the individual lens systems telecentric on the object side and implementing a light-shielding design to prevent stray light from adjacent apertures without using light-shielding walls. This paper discusses not only the design methodology but also the prototyping process and the results of image evaluations.