Ultrathin digital camera inspired by xenos peckii vision

Abstract

Arthropods obtain the visual information of surroundings by hundreds to the thousands of integrated optical units called ommatidia. Spherically arranged ommatidia receive light from their own direction with small ac-ceptance angles. The panoramic mosaic image is formed by combing detected optical signals from each ommatidium. The optical schemes are expected to have figures-of-merit in field-of-view, visual acuity, high sensitivity of motion, polarization detection and spectral sensitivity. Nature provides ten typical and one ad-ditional unusual optical designs of compound eyes. The distinctive features include seven apposition, three superposition, and one unusual eye, which is Xenos peckii’s eye. The anatomical features and the imaging principle of Xenos Peckii’s eye is different from conven-tional compound eyes. The optical unit of Xenos Peckii’s eye consists of a large convex lens and multiple photoreceptor cells, whereas that of apposition compound eye has one to several photoreceptor cells in a single unit. Each optical unit called eyelet detects partial image of the total field of view with improved spatial resolution and sensitivity compared to typical compound eyes. In this work, ultrathin digital camera inspired by Xenos peckii vision is designed, fabricated, and optically characterized. Experimental design methods using planar micro-optics were proposed for development of artificial compound eyes. Optical properties of compound eyes are essential information for development of com-pound eye inspired optical systems. However, the individual scheme was not well researched for engineering applications even though it has some attractive figures-of-merit for sustainable life style. Cross-section of natural compound eyes was patterned on a planar substrate, which provides not only optical properties of natural compound eyes but also design guidelines for compound inspired optical systems. A natural omma-tidium can be emulated by a cylindrical microlens, a conical structure, a waveguide, and a photodetector on a planar substrate. Light propagation inside the individual ommatidium was directly visualized by defining the whole structures with Rhodamine 6G doped photosensitive polymer resin. Ultrathin digital camera inspired by Xenos peckii vision was developed and integrated with a com-mercialized image sensor. A single channel of the camera includes a microprism to tilt the optical axis, a mi-crolens to focus the light from the microprism and an aperture to block the light from adjacent channels. The microprism arrays were implemented by using imprinting process using a ball lens and backside lithography with prepatterned metal mask. And the light absorbing structures were formed using black polymer to prevent the entrance of light from side wall of the microprism. Each microprism has different viewing direction re-spective to its location, allowing omnidirectional light detection. The channels detect portion of the total field of view like that of Xenos peckii, and the captured images are assembled in the image processing step. Micro-lens arrays formed on a flat substrate result in a flat image plane, which enables direct integration with a commercially available image sensor. In summary, this work demonstrates ultrathin digital camera inspired by Xenos peckii vision. Planar emulated cross-section of compound eyes was proposed to provide design rules for compound eye inspired optical systems. The proposed camera can create new opportunities for miniaturized imaging system such as surveillance and reconnaissance instruments, imaging apparatus of endoscopy, mobile devices, and other optical sensors.