Fabrication of curved microlens array using a drop-on-demand droplet generator and polydimethylsiloxane replica mold

Abstract

A simple approach was demonstrated to fabricate the curved microlens array (MLA) using a drop-on-demand (DOD) droplet generator and a polydimethylsiloxane (PDMS) replica mold. The planar microlens array (planar MLA) was fabricated using a simple and cost-effective DOD droplet generator, and then the curved MLA was fabricated by multiple replication processes. The PDMS elastomer membrane mold replicated from the planar MLA was used to transfer the microlenses from a planar substrate onto a spherical surface. The NORLAND65 (NOA65) optical adhesive was chosen to be the material of the curved MLA due to its good optical properties. The curved MLA, whose radii of curvature of the spherical surface were approximately 5.1 and 1.8 mm, was fabricated. The morphology damage during the replication process was avoided by the surface treatment of the PDMS elastomer membrane mold and the deformation of the curved microlens was analyzed and was ranged from 2.1% to 8.5%. The surface quality of the curved microlenses was measured by a white light interferometer and an atomic force microscope and the results showed that the arithmetical mean deviation of the profile Ra was 0.54 nm with a 2×2-μm2 scanned area, while the resultant surface showed an excellent surface smoothness. The imaging and focus performance of the curved MLA were measured by a projection experiment. The experimental results demonstrated a high potential for curved MLA being applied to scale-invariant processing, robot vision, and fast motion detection.