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

A novel method is proposed to fabricate refractive micro lens array using d ichromate gelatin (DCG) and an enzyme. DCG has optical properties similar t o glass but is sensitive to UV light. The enzyme solution is used to develo p the optically exposed DCG instead of a conventional water-isopropanol dev eloper, which greatly enhances the surface relief depth. The continuous sur face relief structure is realized by a coded grey-tone mask. A computer pro gram 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 transferre d to a substrate material, the fabricated DCG micro lens array can be direc tly used as an optical element. The new process opens a new route of micro lens fabrication, which is simple and low cost. (C) 2001 Elsevier Science B Y All rights reserved.