Efficient Color Filters Based on Fano-Like Guided-Mode Resonances in Photonic Crystal Slabs

We numerically report designs of color filters comprising of 2-D photonic crystal (2D-PhC) slabs of square lattice of air holes. The filter principle is based on excited Fano-like guided-mode resonances (GMRs) in the visible regime with high-quality factor (Q-factor) and low reflection sidebands. The 2D-PhC slab architecture influence on its spectroscopic property is comprehensively investigated. We introduce an alternative PhC lattice, which is formed by introducing an additional hole in each unit cell to enhance the light confinement in the waveguide slab, as such the induced Fano-like GMRs' Q-factor is significantly increased about two orders of magnitude compared to the traditional PhC without additional holes. At Fano-like GMRs, two in-plane waves oscillate toward the opposite directions with a phase difference of π. The radiated fields of these waves strongly cancel each other in the far field, and the coupling between the waveguiding slab and the incident light is dramatically reduced resulting in the high Q-factor of the Fano-like GMR in the introduced PhC slab. As a result, the 2D-PhC slab excited Fano-like GMRs in this work may find fascinating applications in optical filters, optical imaging, optical switching, and so on.