Single-step optical realization of bio-inspired dual-periodic motheye and gradient-index-array photonic structures

This Letter demonstrates a single-step optical realization method for hexagonal and square lattice-based dual periodic motheye and gradient-index-array photonic structures over large areas. Computed phase mask of gradient interference patterns are used as inputs to a phase-only spatial light modulator (SLM), and the first-order diffracting beams are coherently superposed with the help of a 2f-2f Fourier filtering setup to avoid complex optical geometry for generation and control of individual beams. The simulated interference patterns are verified experimentally through a CMOS camera. The fabricated micro-structures on a positive photoresist are shown to have a major periodicity of 638 mu m and minor periodicity of 25.2 mu m, with the air hole diameter varying from 22.7 to 6.9 mu m along the X and Y axes. The depth of the fabricated structure gradually varies from 4.203 mu m at the center to 1.818 mu m at the corner. These structures may be scaled down to submicron features that can show improved anti-reflection properties for solar energy harvesting and GRIN lens for optical wavelength region. (C) 2016 Optical Society of America