Study of optimal filler size for high performance polymer-filler composite optical reflectors

Abstract

Polymer-based diffuse reflectors are cost-effective and high performance alternatives to metallic reflectors and multilayered dielectric mirrors in optical and photonic modules. In this study, we optimized the reflectance of high performance polymer-based reflectors by controlling filler particle size. We use a simple analytical model to investigate the critical size of inorganic fillers required to obtain the highest reflectance with a lower filler volume fraction and reflector thickness. The key model predictions show good agreement with our experimental data using Al2O3-silicone and TiO2-silicone composite reflectors. Our results demonstrate for the first time that for inorganic fillers, the effect of filler size on reflectance is non-monotonic, and a critical filler size ranging from one submicron to several microns provides the maximum reflectance. We observed a 50% difference in optical reflectance between 1 micron and 35 micron Al2O3 at 0.1 volume fraction. A significant improvement in reflectance for polymer-filler reflectors can be realized by utilizing optimized filler size, in order to increase the performance-price ratio for optical and photonic devices.