Plasmonic nano-focusing enhancement of nano-rhombus-shaped resonators in the sub-diffraction limit for highly efficient lightwave collection

Abstract

A kind of optical metasurface composed of arrayed nano-rhombus-shaped resonators is proposed. The metasurface as an arrayed optical antenna for highly efficient collecting incident lightwaves, can be utilized to perform light absorption and nano-focusing. The absorption peak can be modulated in a relatively broad spectral range only by adjusting the thickness of the functioned silver film coated. For the same thickness parameter, the key surface plasmons are effectively excited by incident lightwaves polarized along the short axis of the nano-rhombus can broaden the modulated spectral range compared to that along the long axis. Compared with a single nano-rhombus-aperture, a double nano-rhombus-shaped composite architecture (DNRCA) predicts a higher light absorption peak and a stronger near-field lightwave converging. The resonators present a dipole of resonant oscillation through compressing incident lightwaves into a resonant cavity with a very small gap, and then the net charges distribute over two opposite sidewalls of a single cavity. The coupling oscillation becomes stronger with the narrower air gap of the cavity. The achieved near-field light converging presents a typical focusing spot with a minimum size of ∼21 nm, which is one order of magnitude smaller than the incident wavelength of 633 nm, so as to greatly break the traditional diffraction limit.