Sol-Gel Approaches to Photonic Crystal Systems

Abstract

A prerequisite for an efficient ”molding the flow of light” by photonic crystals is the molding of materials in desired nanostructures. Very often, conventional materials and processing techniques cannot fulfill the theoretical requirements for the materials and structures. Sol-gel methods enable material processing in opal pores and the controlled introduction of sub-wavelength pores into the materials by the use of molecular or supramolecular templates. The porosity can be used for lowering the refractive index, for soft processing of the materials and for stress relaxation. Examples for this approach are ultra-low refractive index films used as support for 2D photonic crystals, inverse opals with a skeleton-like unit cell filling and ferroelectric films with high transparency. In detail, we describe mesoporous silica films with a refractive index of 1.14 for use in 2D photonic crystal waveguide systems and the structure tuning possibilities of inverse opals.