Enhancement of near-field subwavelength focusing using a solid immersion Fresnel zone plate with radially polarized incidence

Abstract

A solid immersion Fresnel zone plate (SI-FZP) is designed, and its near-field diffraction characteristics are analyzed using the vector angular spectrum (VAS) method. The analytical VAS model of formulism for the electric field vector transmitted from a binary amplitude and/or phase circular SI-FZP is obtained for any polarization of incidence. Numerical calculations show that, when the solid film immersing a high-numerical-aperture FZP is truncated close to the FZP’s focus in a single homogeneous medium, the focusing intensity in the vicinity of the SI-FZP–air interface can be improved dozens of times in magnitude for radially polarized incidence, compared with the FZP’s far-field focusing in the single medium without an interface. The validity of the proposed analytical VAS model of formulism to analyze SI-FZP’s diffraction problems has been affirmed by comparison with numerical results obtained by the finite-difference time-domain simulation.