Subdiffraction focusing lens based on quadrangular-frustum pyramid-shaped metasurface

In order to realize the function of subdiffraction focusing using a single flat lens, a special metalens is proposed to modulate the circularly polarized light. Initially, the analyses indicate that the phase shift can cover [0, 2 pi] by changing the rotation angle of a quadrangular-frustum pyramid-shaped structure from 0 degrees to 180 degrees, while the average amplitude transmittance can reach 96% at the wavelength of lambda = 1550 nm. Then, a flat metalens is designed by carefully arranging the quadrangular-frustum pyramid-shaped structures. The simulated results show that a focal spot could be obtained at the focal length of about f = 2.87 lambda, and the focusing efficiency is similar to 14.9%. Meanwhile, the full width at half maximum (FWHM) of the focusing spot is only 0.48 lambda, which is smaller than the diffraction limit. Furthermore, this designed metalens can function comparatively with a conventional lens in one-to-one imaging. (C) 2019 Optical Society of America