Light capsules shaped by curvilinear meta-surfaces

Abstract

We propose a simple yet efficient method for generating in-plane hollow beams with a nearly-full circular light shell without the contribution of backward propagating waves. The method relies on modulating the phase in the near field of a centro-symmetric optical wavefront, such as that from a high-numerical-aperture focused wave field. We illustrate how beam acceleration may be carried out by using an ultranarrow non-flat meta-surface formed by engineered plasmonic nanoslits. A mirror-symmetric, with respect to the optical axis, circular caustic surface is numerically demonstrated that can be used as an optical bottle.

Metacoatings for wavelength-scale, high-numerical-aperture plano–concave focusing lenses

“…However, planoconcave cylindrical lenses may benefit from simplicity in the fabrication of the active metacoating if for instance their elementary units should not be patterned along the cylinder axis. A subwavelength metallic film of thickness d λ including nanoslits with controlled width proved to be good candidates for a tunable phase manipulation not only for spherical wavefronts [32] but also to accelerate focal beams and to create light capsules [25]- [27]. The resulting metacoating can be considered as a graded-index uniaxial metamaterial by simply altering the metal filling fraction f = wm/(wm + w d ) along the corresponding spatial coordinates, y and θ, where w d and wm stand for the width of the slit and the metallic segment, respectively.…”

“…In such manner an aplanatic metasurface patterned on a spherical substrate has been proposed to focus light without coma and spherical aberrations [21]. The concept of metamaterials with engineered dispersion in curvilinear coordinates, with coaxial and concentric geometries, has been extensively exploited for instance in hyperlensing [22]- [24] Previously we presented on a design of non-planar metacoatings composed of subwavelength metal-dielectric arrays to accelerate optical waves in the near field [25]- [27]. These nanostructures allow to grade ultrahigh indices of refraction together with high transmissivity, demonstrating controllable phase and amplitude responses over subwavelength propagation ranges for TM-polarized waves.…”