Optical properties of PMMA inverse opal structures with anisotropic geometries by stretching

The fabrication of three-dimensional periodic microstructures with strong anisotropic geometries is important for nanophotonic devices including photonic crystals and hyperbolic metamaterials. In this study, a simple method using self-organizing colloidal inverse opals of PMMA with directional tensile deformation by stretching was successfully constructed in the temperature range 100 °C–115 °C. Reflection spectroscopy was used for investigating the photonic bandgap of the PMMA inverse opal with anisotropic geometries in anisotropic different extents. The wavelengths of the photonic band gap were related to both the length of the pores in long-axis and short-axis of pores of the inverse opals. The wavelength changes of the photonic band gap significantly affected by the length variation in the short-axis. The anisotropic optical properties were also observed when Ag and Pt were deposited onto the top surface or conformally coated onto the interior interfaces of the anisotropic inverse opals. The structures with higher anisotropic ratios showed stronger variations in the wavelengths of the reflection valleys according to the surface plasmonic polarizations and cut-off frequencies with varying polarization angles of incident light. Moreover, the PMMA inverse opals conformally coated with metals presented indefinite dielectric properties in the visible or near-infrared wavelength region.