Abstract
Curved compound eyes have generated great interest owing to the wide field of view but the application of devices is hindered for the lack of proper detectors. One-lens curved compound eyes with multi-focal microlenses provide a solution for wide field imaging integrated in a commercial photo-detector. However, it is still a challenge for manufacturing this kind of compound eye. In this paper, a rapid and accurate method is proposed by a combination of photolithography, hot embossing, soft photolithography, and gas-assisted deformation techniques. Microlens arrays with different focal lengths were firstly obtained on a polymer, and then the planar structure was converted to the curved surface. A total of 581 compound eyes with diameters ranging from 152.8 µm to 240.9 µm were successfully obtained on one curved surface within a few hours, and the field of view of the compound eyes exceeded 108°. To verify the characteristics of the fabricated compound eyes, morphology deviation was measured by a probe profile and a scanning electron microscope. The optical performance and imaging capability were also tested and analyzed. As a result, the ommatidia made up of microlenses showed not only high accuracy in morphology, but also imaging uniformity on a focal plane. This flexible massive fabrication of compound eyes indicates great potential for miniaturized imaging systems.
Highlights
As an increasingly important optical element, a microlens array (MLA) is characterized by its small size, light weight, and compactability. It provides a universal approach for compact micro-optics systems and is widely used in liquid crystal devices [1,2], laser beam homogenization [3,4], naked-eye 3D displays [5], and artificial compound eyes [6,7,8,9]
Curved artificial compound eyes have generated more attention recently owing to their large field of view and low aberration or distortion
A variety of manufacturing methods have been proposed to fabricate curved artificial compound eyes, including but not limited to laser lithography technology [10], ultra-precision machining [11,12], hydrogel shrinkage [13], two-photon polymerization [14], bottom-up technology [15,16], thermal reflow of two different polymeric materials [17], and membrane deformation of polymers [18] assisted by differential air pressure [19,20,21] or bending ball [22,23,24]
Summary
As an increasingly important optical element, a microlens array (MLA) is characterized by its small size, light weight, and compactability. Because the focal plane of arthropod -inspired compound eyes is arranged on a curve instead of a planar substrate, some approaches were used to try to modify the detectors by integrating the detection and microlens arrays [25] or stacking, cutting, and curving the detector planes [26] Another prevailing strategy was to add an optical relay that steered incident rays and formed images on commercial flat detectors, such as freeform prisms [27,28], sets of lenses [29,30], and optical fibers [19,31]. Contactless hot embossing is considered to be a versatile one-step technique to prepare MLAs regardless of the quality of the molds’ inner relief, applied in mass production of microlens arrays [37,38], and the radius of the curvature can be precisely controlled by process parameters This method demonstrates the potential of making microlenses with multiple focal lengths. The geometrical morphology and optical properties were characterized and an imaging contrast experiment was carried out with a plane detector
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