Evaluation of resist molds formed for fabricating micro-lens arrays and practicability of replicated epoxy resin lenses

Abstract

A new fabrication method of micro-lens arrays with element lens diameters of 20-50 μm was developed in the past research. In the method, epoxy micro-lens arrays are replicated using concave resist patterns as molds. In this paper, resist mold pattern profiles were investigated again in detail, and model curves to be fitted to pattern cross sections were looked over again. As a result, it was found that cross section curves of resist mold patterns were very accurately modeled by decomposing each curve into three parts of a central circular concave arc, a peripheral circular convex arc, and a tangential line connecting them. For this reason, using the new fitting curves, how parallel light rays incident in an element lens were refracted at the lens surface, and concentrated in a spot were investigated. It was clarified by the ray trace that parallel light rays were efficiently concentrated in a considerably small light spots by grace of the tangential line parts. Next, the ray trace results were compared with the experimental results. A micro-lens array fabricated under the same conditions was illuminated by a parallel light ray flux. As a result, the position where the traced rays were concentrated almost coincided with the position obtained experimentally. The diameters of concentrated light spots estimated by the ray trace also almost coincided with the actually observed ones. Thus, optical characteristics of microlens arrays fabricated by the new method were adequately qualified. The new method will be useful.