Fabrication and Characterization of Three-Dimensional Microlens Arrays in Sol-Gel Glass

Abstract

We propose a new replication process for the realization of thick microlenses in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ SiO_2$</tex> glass with low organic content. We start by replicating an array of cylindrical micropillars made in SU-8 negative photoresist (Microchem) into poly-dimethylsiloxane (PDMS). The PDMS replica is filled with a photoresist (Clariant AZ 9260), applied to a glass substrate and soft-baked. After demoulding, we obtain cylindrical pillars that are given a dome-like shape by a thermal softening. This structure is used as a master in a second PDMS replication step. An in-house developed sol-gel glass material with low organic content is then poured in the second PDMS replica and subsequently thermally treated to obtain an array of thick, dense and crack-free microlenses. We characterize the shrinkage and the surface roughness of the microlenses. Using imaging of millimeter-size objects in an optical microscope setup, we characterize basic optical properties of the lenses, like focal length, magnification, and distribution of the light intensity around the focal plane.1741