Numerical analysis of subwavelength focusing using a silicon cylinder

The analysis of the impact of variations in the size of a silicon micro-cylinder with a subwavelength radius on the diffraction of circularly polarized Gaussian beams was performed using a finite-difference time-domain (FDTD) method. It is numerically shown that a Gaussian beam can be focused near the surface of the element in a light spot, whose size at full-width at half-maximum of the intensity is 0.25λ. It is demonstrated that the silicon cylinder illuminated by a laser beam with a vortex phase singularity of the first order forms a light spot, with its central part mainly formed by the longitudinal component of the electric field. (FWHM = 0.29λ).