All-optical fabrication of 2D and 3D photonic microstructures in polymeric materials
We present here two approaches for the fabrication of 2D and 3D optical structures. The first one is a step-by-step fabrication process of 3D structures using thin relief gratings (stacks of thin 1D or 2D gratings). Azobenzene containing materials for the surface relief inscription have been used in the step-by-step procedure, where after holographic inscription of desired relief structure and coverage with spacer layer another correlated relief structure has been written in the next active layer etc. The method provides full flexibility of the structure type and parameters including different gratings in different layers (hierarchical structures). A technique to produce hexagonal relief gratings of enlarged diameter which can be used for layer-by-layer photonic structures is developed. The second approach is a multi-beam holographic recording using special phase masks. Such mask consists of three phase gratings arranged in plane equilateral triangle geometry with gratings vectors at 120° to each other. A simple method of fabrication of well-adjusted mask with rather high diffraction efficiency is developed. Hexagonal 2D surface relief and 3D volume phase structures were fabricated by a single laser beam exposure using UV or visible wavelengths (depending on the material) through the mask. Azobenzene containing materials and photopolymers, including new specially designed one, were used as holographic materials.