Artificial Ommatidia Research Articles

Motion detection based on 3D-printed compound eyes

A biologically inspired compound eye system is fabricated for the detection of object motion without the need for sophisticated image processing. The array of the artificial optical unit, called ommatidium, structurally and functionally mimics the natural compound eyes for motion detection. Each artificial ommatidium consists of polymer lenses, a light-guiding polymer cone, a 3D printing cladding, and a light intensity sensor to measure the change of light intensity during motion detection. To simplify the signal processing and improve the system reliability, low-cost light sensors, instead of CMOS/CCD arrays, are used for measuring the light intensity changes caused by object movement. The distance and speed of a moving metal ball of a pendulum were measured using the compound eye system. The measured results agree well with the theoretical analyses. The error between the measured and calculated speed is less than 2%.

One-lens camera using a biologically based artificial compound eye with multiple focal lengths

This work presents the fabrication of a one-lens camera using a biologically inspired artificial compound eye with multiple focal lengths. Traditional camera designs that consist of many separated lenses are difficult to assemble due to tight tolerance. The one-lens camera design is demonstrated experimentally in this work to avoid tolerance buildups. This structure is based on the principles of both the human eye as well as an insect’s compound eye. The artificial compound eye is a curved hexagonal microlens array, like an ommatidial array, wherein each artificial ommatidium collects light with a small angular acceptance. The ommatidia, in a typical hexagonal arrangement of 37 lenses, are arranged across a hemispherical photopolymer dome. The curved hexagonal array helps us to achieve a compact and wide field-of-view camera module. The fabrication process for the curved array is divided into two parts: creation of a planar hexagonal multi-lens array, and a replication process. To create the planar array, we use inkjet printing technology with the hydrophilic confinement effect to establish microlens shapes with different profiles. Next, the replication process converts the planar array into a curved shape. The spherical configuration of the hexagonal array is accomplished by applying the template architecture to a reconfigurable surface shape, that is, a photopolymer duplication using a deformed elastomer membrane with the hexagonal array pattern. In our experimental demonstration, microlenses in four rings with different focal lengths are fabricated on a single hemispherical lens with radius of curvature of 2.4 mm. The thickness of our proposed system is 3.04 mm, the f-number is 1.68, and the diagonal field of view is 92.6 deg. Above all, our presented camera module system uses a single one-piece lens.

Hardware architecture and cutting-edge assembly process of a tiny curved compound eye.

The demand for bendable sensors increases constantly in the challenging field of soft and micro-scale robotics. We present here, in more detail, the flexible, functional, insect-inspired curved artificial compound eye (CurvACE) that was previously introduced in the Proceedings of the National Academy of Sciences (PNAS, 2013). This cylindrically-bent sensor with a large panoramic field-of-view of 180° × 60° composed of 630 artificial ommatidia weighs only 1.75 g, is extremely compact and power-lean (0.9 W), while it achieves unique visual motion sensing performance (1950 frames per second) in a five-decade range of illuminance. In particular, this paper details the innovative Very Large Scale Integration (VLSI) sensing layout, the accurate assembly fabrication process, the innovative, new fast read-out interface, as well as the auto-adaptive dynamic response of the CurvACE sensor. Starting from photodetectors and microoptics on wafer substrates and flexible printed circuit board, the complete assembly of CurvACE was performed in a planar configuration, ensuring high alignment accuracy and compatibility with state-of-the art assembling processes. The characteristics of the photodetector of one artificial ommatidium have been assessed in terms of their dynamic response to light steps. We also characterized the local auto-adaptability of CurvACE photodetectors in response to large illuminance changes: this feature will certainly be of great interest for future applications in real indoor and outdoor environments.

Digital cameras with designs inspired by the arthropod eye

In arthropods, evolution has created a remarkably sophisticated class of imaging systems, with a wide-angle field of view, low aberrations, high acuity to motion and an infinite depth of field. A challenge in building digital cameras with the hemispherical, compound apposition layouts of arthropod eyes is that essential design requirements cannot be met with existing planar sensor technologies or conventional optics. Here we present materials, mechanics and integration schemes that afford scalable pathways to working, arthropod-inspired cameras with nearly full hemispherical shapes (about 160 degrees). Their surfaces are densely populated by imaging elements (artificial ommatidia), which are comparable in number (180) to those of the eyes of fire ants (Solenopsis fugax) and bark beetles (Hylastes nigrinus). The devices combine elastomeric compound optical elements with deformable arrays of thin silicon photodetectors into integrated sheets that can be elastically transformed from the planar geometries in which they are fabricated to hemispherical shapes for integration into apposition cameras. Our imaging results and quantitative ray-tracing-based simulations illustrate key features of operation. These general strategies seem to be applicable to other compound eye devices, such as those inspired by moths and lacewings (refracting superposition eyes), lobster and shrimp (reflecting superposition eyes), and houseflies (neural superposition eyes).

Microfabricated ommatidia using a laser induced self-writing process for high resolution artificial compound eye optical systems

A microfabricated compound eye, comparable to a natural compound eye shows a spherical arrangement of integrated optical units called artificial ommatidia. Each consists of a self-aligned microlens and waveguide. The increase of waveguide length is imperative to obtain high resolution images through an artificial compound eye for wide field-of - view imaging as well as fast motion detection. This work presents an effective method for increasing the waveguide length of artificial ommatidium using a laser induced self-writing process in a photosensitive polymer resin. The numerical and experimental results show the uniform formation of waveguides and the increment of waveguide length over 850 microm.

Biologically Inspired Artificial Compound Eyes

This work presents the fabrication of biologically inspired artificial compound eyes. The artificial ommatidium, like that of an insect's compound eyes, consists of a refractive polymer microlens, a light-guiding polymer cone, and a self-aligned waveguide to collect light with a small angular acceptance. The ommatidia are omnidirectionally arranged along a hemispherical polymer dome such that they provide a wide field of view similar to that of a natural compound eye. The spherical configuration of the microlenses is accomplished by reconfigurable microtemplating, that is, polymer replication using the deformed elastomer membrane with microlens patterns. The formation of polymer waveguides self-aligned with microlenses is also realized by a self-writing process in a photosensitive polymer resin. The angular acceptance is directly measured by three-dimensional optical sectioning with a confocal microscope, and the detailed optical characteristics are studied in comparison with a natural compound eye.

Artificial ommatidia by self-aligned microlenses and waveguides

We report the fabrication of artificial ommatidia, the imaging units of insects' compound eyes, by use of polymer integrated optics. These biomimetic structures are obtained by configuring microlenses to play dual roles for self-writing of waveguides (during the fabrication) and collection of light (during the operation). The artificial ommatidium, consisting of a microlens, a spacer, and a waveguide, directly resembles the structure of its biological counterpart. Optical characterizations reveal single-peak angular sensitivity with a +/- 0.75 degrees acceptance angle that is comparable to those found in nature. Using geometric and physical optics, we also investigate the relationship between angular sensitivity and the geometry of artificial ommatidia.