Precision Replication of Co-Molded Meso and Micro Optics Through Injection Molding

Abstract

The objective of the research reported here is to extend the limits of current optical production techniques for complex, thermally-stable, precise optical components produced in large volume. The goals of this research address the challenges on two fronts 1) injection molding of polymer lenses, and 2) molding of polymer elements directly onto stable substrates.

The first goal was addressed through an increased understanding of the injection molding process in the replication of micro optics. Precision molds were produced with optical features of varying size, shape, step height, and aspect ratio. These features included spherical and Fresnel lenses, a blaze diffraction grating, and a wedding cake. Feature pitch was as small as 10um and step heights as small as 1.25um. To gain increased understanding, a partial factorial screening design of experiment was performed to discover the molding factors (process variables) with the greatest effect on the replication of micro optics. These experiments showed mold temperature and screw rotation speed to have the greatest effects on the accurate replication of meso and micro optics.

The second challenge, the thermal instability of polymer lenses, has been addressed through research of the co-molding of these optics directly onto thermally stable substrates. Challenges included the modification of properties at the polymer-substrate interface, the large mismatch in coefficients of thermal expansion between the materials, and mold design factors for using substrates in the injection mold. In the experiments, interface adhesion was found to be increased through the use of organofunctional silanes, and co-molding experiments revealed that acrylic lenses had the best adhesion to specially cleaned soda lime glass.