Angular and polarization properties of cross-holes nanostructured metallic filters.

It has been shown in literature that cross-shaped holes arrays can be made insensitive to polarization at normal incidence, and can even feature good stability for off-normal incidence. In this work we look for the optimal design rules to obtain high spectral stability conditions in the visible for those structures, through a complete review of all geometrical parameters using CMOS-compatible materials. Rigorous Coupled Wave Analysis (RCWA) simulations have been used to identify the most-impacting parameters and to determine typical ranges allowing for the realization of low-color errors image sensors whatever the light incidence. It appears that the two main parameters are the ratio of the arm width to the arm length of the crosses and the distance between crosses, which both have to be low to ensure stable responses of the filters. We demonstrate the results with CIE chromaticity diagrams reporting the responses of a RGB filter designed with the established rules under various illumination conditions.