Refractive micro lens array made of dichromate gelatin with gray-tone photolithography

Abstract

A novel method is proposed to fabricate refractive micro lens array using dichromate gelatin (DCG) and an enzyme. DCG has optical properties similar to glass but is sensitive to UV light. The enzyme solution is used to develop the optically exposed DCG instead of a conventional water–isopropanol developer, which greatly enhances the surface relief depth. The continuous surface relief structure is realized by a coded grey-tone mask. A computer program has been developed to code an arbitrary 3D surface relief shape into a grey-tone mask design. The DCG properties and the lithography process are described. The grey-tone coding principle is presented. Unlike the current processes where patterned photoresist relief structure has to be transferred to a substrate material, the fabricated DCG micro lens array can be directly used as an optical element. The new process opens a new route of micro lens fabrication, which is simple and low cost.