A study on diffraction light spots with absolute central symmetry through Pancharatnam-Berry metasurface

Abstract

Traditional diffractive optical elements (DOEs) usually use random arrangement as the initial phase, and the asymmetric diffraction structure is obtained by optimization iteration. The processing error of asymmetric diffraction structure will introduce irregular speckle noise and expand the influence of structural mutation on the uniformity of diffraction spot, which is difficult to meet the requirements of absolute centrosymmetric diffraction. In this paper, a diffractive metasurface based on Pancharatnam-Berry (PB) phase is proposed. Using the chiral sensitivity of the PB phase to circularly polarized light, the absolute centrosymmetric spot modulation is realized by constructing the mirror phase. Through theoretical research and simulation analysis, the absolute centrosymmetric characteristics of one-dimensional diffractive metasurfaces are demonstrated. A two-dimensional diffraction beam-splitting metasurface with a wavelength of 632 nm was fabricated by electron beam lithography. The relationship between spot uniformity and central symmetry of diffraction orders when linearly polarized light (LP) is incident is experimentally analyzed, which expands the absolute central symmetry research of two-dimensional diffraction metasurfaces. Subsequently, according to the characteristic that the spot symmetry is modulated independently with the dimension, the tilt measurement of the misalignment system is carried out. Experiments show that this method can be used as a candidate method for optical system calibration.