Design and characteristics of polarization-insensitive resonant gratings for color filtering

A method of designing polarization-insensitive color filters with guided-mode resonance grating is presented. The influence of incident conditions on exciting waveguide mode is investigated, and we find that polarization insensitivity may occur at the full conical incidence. Using rigorous coupled-wave analysis, we mainly analyze the effects of waveguide thickness and fill factor on the diffracted efficiency of the grating filter. The final structural parameters of the devices for three primary colors are collected after optimization, and the calculated results show that the spectral reflectance of each color filter is basically identical for different polarization states of incident light. Moreover, field analysis by the finite-difference time-domain technique indicates that two symmetric modes are excited between the waveguide layer and substrate under full conical incidence, which is coincident with the previous theoretical study. The reported work will eliminate the restriction of polarization-dependence of color filters and greatly expand their application range.