Enhanced Far-Field Focusing by Plasmonic Lens Under Radially Polarized Beam Illumination

A plasmonic lens with coupling annular grooves is proposed to achieve enhanced far-field focusing performance. Based on the finite difference time domain (FDTD) method, we demonstrate that a focal beam could be obtained under a radially polarized light illumination. The obtained focal length and working distance range from 3.1 to 3.6 mu m and 1.7 to 2.1 mu m, respectively. The full-width at half-maximum (FWHM) of the focal spot is about 0.8 lambda (i) and the overall field enhancement factor is improved to be similar to 3.9.