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Fabrication of 2D photonic crystals with micron to submicron hexagonal lattices using single-exposure holographic technique

A single-exposure holographic technique for fabricating 2-dimensional photonic crystals (PCs) with hexagonal lattices is presented. A specially made holographic optical element (HOE), which consists of three holographic gratings, is used to generate three interference beams simultaneously under the illumination of a single laser beam. Theoretical analysis indicates that by selecting appropriate grating period and illuminating wavelength, the hexagonal lattice patterns formed by the interference of the three beams can have the lattice constants in the range from micron to sub-micron. Moreover, to obtain uniform lattice pattern with high contrast, the gratings in the HOE must have proper grating shape and depth. In the experiment, hexagonal lattices with lattice constants from 5 μm to 620 nm were fabricated in photoresist using the method. The patterned photoresist layers can be used as the masks to generate PCs in semiconductor materials through dry or wet etchings.