Optical analog of compound eyes using planar micro-optics

Abstract

A natural compound eye has a spherical set of integrated optical units called ommatidia, whose each individual unit consists of a facet lens, a crystalline cone, a light-guiding rhabdom, and a photoreceptor. Each ommatidium looks slightly different direction, wide field-of-view (FOV) image and fast motion detection can be obtained. Due to its attractive advantages, there have been many efforts to mimic its optical structure to apply in imaging system. To develop high resolution imaging system using a natural compound eye, not only its structure but also its optical characteristics should be mimicked. In previous work, 3D structure of artificial compound eye which comprising about 8,400 ommatidia was implemented using self-aligned microlens and waveguide, but it’s not easy to characterize its optical characteristics as a function of geometry parameter such as F-number of microlens, afocal effect, waveguide diameter, etc. In this work, optical analog of compound eyes in nature is conducted using planar microoptics. The diameter of the microlens is $25 \mu m$, F-number is 1.8, and the waveguide diameter is $3 \mu m$ , which are typical sizes of the natural compound eyes. Using a simple photolithographic process with a Rhodamine 6G dye doped photosensitive polymer resin, the ommatidium can be mimicked on a glass substrate for visualizing the light propagation inside a planar artificial compound eye (ACE). Under directional illumination, a spherical arrangement of the artificial ommatidia contributes to the angular acceptance measurement. Angular sensitivity function of simple apposition, afocal apposition, and transparent apposition eye is measured and characterized. The afocal apposition eye in nature has narrower angular sensitivity function than the conventional apposition eye due to angular magnification in crystalline cone. And this is confirmed experimentally using planar ACE. The measured angular acceptance of an afocal apposition is 4° and that of a ...