Discontinuous space variant sub-wavelength structures for generating radially polarized light in visible region

摘要

A discontinuous space variant sub-wavelength dielectric grating is designed and fabricated for generating radially polarized light in visible region (λ = 632.8 nm). The design is based on sub-wavelength silicon nitride structures introducing a retardation of π/2 by form birefringence, with space variant orientation of the optical axis. The pattern is divided into concentric ring segments with constant structural parameters, therefore reducing electron-beam writing time significantly. The design avoids the technological challenges encountered in the generation of a continuous space variant grating while maintaining good quality of the resulting polarization mode.