Binary-amplitude modulation based super-oscillatory focusing planar lens for azimuthally polarized wave

Abstract

Tight focus of azimuthally polarized wave finds its applications in optical super-resolution, particle trapping and so on. To overcome the disadvantages of conventional optics, including bulky size and difficult for integration, a binary-amplitude (0, 1) super-oscillatory planar lens is designed for sub-diffraction focusing of azimuthally polarized wave at wavelength of 632.8 nm. The lens radius is 650λ, and its focal length is 200λ. The corresponding numerical aperture is 0.96. The experimental results demonstrate the generation of a hollow spot with circular ring shape on the focal plane. The inner full-width-at-half-maximum of the hollow spot is 0.368λ, smaller than the super-oscillatory criterion (0.398λ), and the maximum sidelobe ratio is about 36.7%. Such planar lenses are easy to fabricate. Their small size and ultra-thin thickness make them promising in system minimization and integration for different applications, such as optical microscopy, optical trapping and ultra-high density data storage.