Fabrication of the 3D BAC-eye
The design of the 3D BAC-eye follows the anatomical structure of an apposition compound eye (Fig. 1a). Each microlens on the BAC-eye has the same function as the corneal facet lens of a natural eye. The cylindrical post and the silicone-elastomer waveguide function as a crystalline cone and a rhabdom, respectively (Fig. 1b). The internal structure of the artificial eye mimics the function of pigment cells to reduce optical crosstalk. The number of ommatidia in the BAC-eye (522) is comparable with that of bark beetles (Dendroctonus rufipennis, average count: 272; Dendroctonus valens, average count: 372), ants (Temnothorax albipennis, average count: 300 (male) and 171 (queens); Brachyponera chinensis, average count: 168 (worker) (Fig. 1c)), and fruit flies (Drosophila melanogaster, average count: 730)47,48,49. Figure 1d shows a top-view SEM image of the BAC-eye. It has a radius of 2.5 mm and its microlenses are hexagonally and omnidirectionally distributed across the hemispherical dome. The most peripheral ommatidia are oriented at ±85° with respect to the vertical axis, extending the viewing angle of the BAC-eye to 170°.