Subwavelength focusing of micro grating-Fresnel lens

The focusing performance of micro grating-Fresnel (G-Fresnel) diffractive optical element is investigated, for the first time, by finite-difference time-domain method based on rigorous electromagnetic theory. The focusing of G-Fresnel lens with different incident wavelength, focal length, and period of grating are explored. Numerical result shows that a subwavelength focusing can be achieved by G-Fresnel lens. Meanwhile, for incident beam with wavelength larger than the period of grating, the transmission of light decreases abruptly. The optical performance is governed by scattering effects from micro G-Fresnel lens. Our results provide very useful information in the field of optical imaging with high resolution and optical precision measurement.