Near-field focusing properties of zone plates in visible regime - New insights

Abstract

Near-field focusing properties of zone plates are investigated in the visible regime by a 3-dimensional finite-difference time-domain method. It is shown that Frensel zone plates (FZPs) with metallic coatings can achieve subwavelength focusing in the visible wavelength. The characteristics of subwavelength focusing are found to be independent of the type of metal coatings used. All the FZPs exhibit similar shift in focal length and depth of focus when compared with classical calculations. These results indicate that plasmonic waves do not contribute to subwavelength focusing. Instead the subwavelength focusing characteristic is attributed to the interference of diffracted evanescent waves from a large numerical aperture. It is found that the near-field focusing of FZPs suppresses higher order foci such that the corresponding diffraction efficiency is improved. The use of phase zone plate structured on glass without opaque coating is proposed to improve the diffraction efficiency of subwavelength focusing.

Application of Surface Plasmon Polaritons in CMOS Digital Imaging

“…FWHMx, is sensitive to the number of zones. Other authors also found the dependence of the focal lengths of a FZP on the zone numbers [34]. A straightforward understanding is that more zones integrated in the PL aperture, i.e.…”

“…However, diffraction may put the usefulness of the microlens in question in sub-2 m pixels [28]. Recent progress in nanotechnology and the theory of plasmonics has led to rapidly growing interest in the implementation of metallic optical elements on a nano-scale for light beam manipulation [29][30][31][32][33][34][35][36][37][38][39]. Especially, lots of theoretical predictions [30][31][32][33][34][35] and experimental demonstration [28,[36][37][38][39] have been reported on both one-dimensional (1D) and 2D PLs.…”

Optimization of transmission and focusing properties of plasmonic nanolenses

“…Through the last decade a lot of work was devoted to plasmonic focusing devices [2] which are in the form of planar metallic layers with holes, slits or surface corrugations either linear or circular [3][4][5][6][7][8][9][10][11]. Such structures, unlike classical, refractive lenses, concentrate light in a two-step process of photon-plasmon and plasmon-photon couplings.…”

“…Such structures, unlike classical, refractive lenses, concentrate light in a two-step process of photon-plasmon and plasmon-photon couplings. Such lenses can be classified as near-field devices concentrating evanescent field in the vicinity of the metal plate due to constructive interference of plasmons efficiently generated on circular grating [4][5], or far-field ones focusing light in the region distant a few wavelength from the lens due to phase matching of propagating beams scattered on the edges of slits or grooves at the back surface [6][7][8][9][10][11][12]. Generation an electromagnetic surface waves is strongly polarization dependent.…”

Design of a meta‐screen for near‐zone field focalization at optical frequencies

“…Even though sub-wavelength focusing at optical frequencies has already been demonstrated through the use of Fresnel Zone plates with metallic coatings [5], what we propose here is a different design, based on the patterning of an opaque surface with a discrete set of dielectric cells, to create an inhomogeneous spatial distribution of the electric permittivity of the screen. In addition, the proposed approach suggests the possibility to achieve a subwavelength desired pattern at arbitrary distances.…”