We designed a kind of new vortex beam generator based on a planar all-dielectric metamaterial in the mid-infrared band. The height of this generator remains constant in the plane, and the effective refractive index increases gradually in the azimuthal direction which depends on subwavelength aperture columns with gradual diameters in the dielectric flat plate. Two types of vortex beam generators including transmissive- and reflective-type generators are designed where the thickness of the latter is half of the former. Simulation results show that both vortex beam generators successfully produce mid-infrared vortex beams with a topological charge number of one. This planar vortex beam generator based on a dielectric metamaterial has the advantages of simple structure, easy processing and low optical absorption.
Qiao et al. (Thu,) studied this question.