Controlling near-field focusing of a mesoscale binary phase plate in an optical radiation field with circular polarization

Binary Fresnel zone plates (ZP) are one of the most frequently used focusing elements inplane optical schemes in micro- and nanophotonics. With a decrease diameter focal distance ZP to meso-wavelength sizes, parameters region begin be significantly influenced by features design (material, thickness, relief depth). The spatial structure spot formed near-field is investigated numerical finite (FEM) simulations transmission plane wave through mesoscale binary phase ZP. We show that there range optimal etching depths ridges thicknesses plate substrate, at which best incident realized terms maximum field intensity minimum size spot. In addition, concept super-focusing with an immersion layer form truncated cone fabricated material proposed, makes it possible focus circularly polarized light into subdiffraction half-width about "lambda"/2n (n refractive index).