Fig. 2: Operating principles and fabrication of the ACEcam.
a Scanning electron microscopy (SEM) image of the conical microlens on an optical fibre. b Top view of the ACEcam light receiving head that uses a 3D-printed dome to host 271 fibre ends. c Photograph of an assembled ACEcam. d Concept of image formation. Using a ‘+‘ line-art pattern as the object (top panel), some fibres receive light from the object (second panel), and this pattern is transmitted from the lens end to the other end of the fibre (third panel). An imaging lens is employed to project the light from the fibre ends to a flat imaging sensor chip (fourth panel top), which is then converted into the final digital image (bottom panel). e Fabrication process flow of conical microlens optical fibres. A template with an array of conical grooves is fabricated by an ultrahigh precision 3D printing method (top panel), then the first PDMS mould is made to obtain convex cones (second panel). Physical vapour deposition and electroplating are then utilised to coat Cu layers on the first PDMS mould to smooth the rough surface of the convex cones and to round the sharp tip of the convex cones (third panel). After the second pattern transfer to get the second PDMS mould, optical adhesive NOA81 is dropped (0.15 μL/drop) into each conical groove by using a microsyringe (fourth panel). Next, an optical fibre buncher is mounted on the second PDMS mould so that optical fibres are well aligned with and submerged into the NOA81 microlenses wells. After UV illumination, each optical fibre end is mounted with a conical microlens, and finally, all fibres are peeled off (bottom panel)
