Fabrication of gapless microlenses on spherical surface by multi-replication process

Abstract

Artificial compound-eye structure has been studied recently due to its great applications of wide field-of-view imaging and backlight modules. However, fabrication process for microstructures on curvilinear surface has a lot of difficulties since traditional fabrication techniques are planar. In this paper, a simple and low-cost method to fabricate microlenses on spherical surface was demonstrated. Microlenses with high fill factor were formed by thermal reflow technique, followed by multiple replication processes to transfer the microlenses from planar substrate onto spherical surface. During the process, we made a curved mold with concave microlenses, which allowed this method to be duplicable easily. Polydimethylsiloxane (PDMS) elastomer was employed as the material of both microlenses and mold due to its flexibility and transparency for visible light. To prevent microlenses from being damaged during the release procedure, surface treatment using trichloro(1H,1H,2H,2H-perfluorooctyl)silane was applied before every replication process. Several PDMS domes covered with hexagonal or square microlenses on the surface were fabricated successfully. The diameter of each microlens was about 200 μm and the pitch of array was 220 μm. The radius of curvature of the spherical surface was about 6.1 mm. The uniformity of microlenses was analyzed through the intensity distribution of focused spots. Imaging performance of microlenses was shown. The curved microlens arrays were combined with image sensor, and clear images of objects at different distance are shown. The experimental results showed a high potential for curved microlens arrays being applied to compact mobile camera lens.

Fabrication and characterization of artificial miniaturized insect compound eyes for imaging

“…Further, until now, only a few methods had been available for fabricating three-dimensional (3D) structures. These included laser lithographic fabrication methods [19,20], semiconductor fabrication techniques [21][22][23][24][25], and hybrid sol-gel methods [26][27][28]. Although biomimetic structures that replicate insect compound eyes can be fabricated by these methods, these techniques need expensive facilities and involve long processing times and complicated fabrication procedures.…”