No abstract

The variation of the refractive index is the key property of photorefractive materials and an important factor that affects photonic crystals. Therefore, photorefractive photonic crystals are interesting optical materials in physics. One of the typical groups of photorefractive materials, polymer dispersed liquid crystals (PMMA, 5CB, and C60), are filled into three dimensional silica colloidal crystals by solventinduced phase separation to fabricate photonic crystals. The stop band shifts to shorter wavelength when a low voltage is applied. By using the z-scan and two-beam coupling technique, several band gap dependent optical properties of photorefractive photonic crystals are studied whilst continuously adjusting the wavelength of the stop band. The third-order nonlinear refractive coefficient is enhanced at the edge of the photonic stop band. The photorefractive diffraction efficiency achieves a maximum value when the stop band wavelength overlaps with the laser beam wavelength.

The development of advanced methods for graphene with nanoscale width and periodic geometries is important to graphene-based electronic and optical devices. Metal inverse opals and opals were used as reliable nanopatterned electrodes for the electrochemical reactions of graphene oxide (GO) films at −0.8 to −1.5 V versus saturated calomel electrode. Graphene with redox patterns was formed by limited reduction time. Reduced GO (RGO) films with deeper surface impress patterns were formed after electrochemical reductions and varied according to the surface geometries of the Ni inverse opals. The resistivity of the RGO using Ni solid films and inverse opals decreased rapidly because a connected RGO formed at the beginning of the reduction. In contrast, the resistivity of RGO reduced by Ni opals did not show a significant decrease in the beginning because of the disconnected reduction. The formed periodic undulations of RGO structures did not show the coupling of optical wavelength, but shifted the stop band of colloidal crystals covered under them.