Two-step resonant diffraction grating designed for three-color separation in Fresnel diffraction region.

A two-step resonant diffraction grating is designed to separate the distributions of the wavelengths of 633, 532, and 488 nm in the Fresnel diffraction field using an analytical solution of the modal method, which can give a physical explanation for mode propagation in the grating region and interference at the interfaces. The energy efficiencies are 76.1% for 633 nm, 83.5% for 532 nm, and 75.6% for 488 nm at TE polarizations. The field distributions are captured by a color CMOS detector with a microscope, and the experimental results show the grating has a good color-separation performance.