Bi-directional Scatter Distribution Function (BSDF) Measurements of Large Area Photonic Crystals

Optical metamaterials, or photonic crystals (PCs), are lattice structures made of two or more materials with different refractive indicies with the structure repeating at a sub-wavelength period. This results in a photonic bandgap within the material, completely rejecting certain wavelengths, similar to an electronic bandgap within a semiconductor. Recent developments have allowed the production of PCs with large areas, suitable for analysis using standard optical techniques. Using a large sample of a two-dimensional PC designed to reject 532nm at normal incidence, we investigated the Bi-directional Scatter Distribution Function (BSDF) of the material using a Complete Angle Scatter Instrument (CASI) with a 544nm laser, with the goal of modeling its BSDF. Despite the difference between the laser and the PC's design wavelengths, several interesting features were apparent, including anomalous reflection and transmission at 22degrees from normal regardless of the incident angle, and strong scattering in all directions for a 22degrees incident angle. Since most computationally efficient BSDF models are parameterizations of measured data, these features drastically increase the difficulty of BSDF modeling as no existing model can account for them.