title: Theoretical analysis and design guideline for focusing subwavelength gratings.
abstract: We propose a planar dielectric reflector with focusing ability using concentric circular subwavelength gratings (CC-SWGs). The two-dimensional focusing ability of CC-SWGs is investigated by the rigorous coupled-wave analysis (RCWA) and finite element method (FEM). By designing the concentric circular pattern of the grating surface, a focusing reflector with high numerical aperture (NA) and high reflectivity is constructed. A CC-SWG reflector with a diameter of 32.6μm and a focal length of 6μm is investigated, which exhibits high focusing ability at normal incidence with a radially polarized plane wave. At the reflection focal plane, the full-width-half-maximum (FWHM) of the electric field intensity is 0.89μm. Numerical aperture value as high as 0.93 is achieved for the reflector with very high reflectivity of 92%.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Duan
authors.forename: Guren
authors.initials: G
authors.lastname: Zhou
authors.forename: Yongqing
authors.initials: Y
authors.lastname: Huang
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Shang
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Ren