Nonpolarizing guided-mode resonant grating filter for oblique incidence

A new type of guided-mode resonant grating filter is described. The filter is independent of polarization state for oblique incidence. The filter has a crossed grating structure, and the plane of incidence on the filter conta ins the symmetric axis of the grating structure. Theoretical considerations and numerical calculations using two-dimensional rigorous coupled-wave ana lysis show that a rhombic lattice structure is suitable to such filters. In this configuration an incident light wave is diffracted into the waveguide and is divided into two propagation modes whose directions are symmetric w ith respect to the plane of incidence. In particular, when the propagation directions of the two modes are perpendicular to each other, the fill facto r of grating structure can be similar to 50%. The filter was designed for a n incident angle:of 45 degrees. Tolerances of setting errors and fabricatio n errors for this filter were estimated by numerical calculations. (C) 2001 Optical Society of America.