Tailoring Orbital Angular Momentum of Light in the Visible Domain with Metallic Metasurfaces

Abstract

ways. One can mention the use of spiral phase plates, [ 3,4 ] computer generated holograms, [ 5,6 ] optical mode conversion, [ 7 ] lasing on higher-order modes of resonators, [ 8 ] light propagation in uniaxial crystals, [ 9,10 ] and space-variant birefringent retarders with formed [ 11 ] or natural [ 12 ] birefringence. Since then, these approaches have been improved and singular photonic technologies have emerged, a large set of products being now available to generate vortex beams. Still, from a practical point of view, mature options remain those relying on bulk and macroscopic optical elements.Quite naturally, research efforts have been made to miniaturize singular optical devices. For instance, femtosecond 3D direct laser writing technique has been proposed to fabricate microscopic spiral phase plates [ 13 ] and easy-prototyping of almost arbitrary singular microoptical elements with standard optical quality is now achievable. [ 14,15 ] On the other hand, self-engineered topological defects of liquid crystals have been shown to behave as small-scale optical vortex generators based on spinorbit interaction of light. In particular, the initial approach based on droplets (1−10 µm diameter) [ 16 ] evolved toward the use of thin (10−100 µm thick) fi lms whose effi ciency, diversity, tunability, and reconfi gurability stand with more than decent fi gures of merit. [17][18][19][20] Another approach consists to functionalize existing integrated optics subsystems with singular features, for instance, by twisting weakly deformed fi bers [ 21 ] or by using corrugated ring microresonators coupled to waveguides. [ 22 ] Of course, above few examples do not aim at providing an exhaustive list of recent progresses and, in order to partly fi ll this gap, one may refer to ref.[ 23 ] for a review of several strategies toward the elaboration of compact singular photonic devices. In particular, the use of ultrathin (i.e., with subwavelength thickness) artifi cially structured surfaces received a growing interest since a few years, as summarized in several recent reviews. [24][25][26][27] The common denominator of these approaches is subwavelength structuring of ultrathin material layer that confers "meta"-properties to it, from which originates the terminology of optical "meta"-surfaces.In this work, we address the particular case of optical vortex generation with topological charge up to | | 10 = , in the visible domain, by using nanostructured metallic thin fi lms following an approach introduced by Hasman's group in the early 2000s in the mid-infrared domain. [ 11 ] The idea consists to benefi t from the spinorbit interaction of light owing to azimuthally varying artifi cially birefringent waveplates made of inhomogeneous subwavelength Submicron-thick gold fi lms endowed with subwavelength patterning allow on-demand topological shaping of light, hence the precise delivery of optical orbital angular momentum. Several kinds of metallic metasurfaces enabling the generation of optical vortices with arbitrary topological charges...

Efficient Vortex Generation in Subwavelength Epsilon-Near-Zero Slabs

“…Similar SOI effects involving Bessel beams have been considered in uniaxial crystals [7] and at reflection and transmission by a planar interface between two homogeneous media [8]. The advent of metamaterials has further increased the SOI research effort [9], mostly in the use of ultra-thin metasurfaces for manipulating the angular momentum of light [10,11] and for vortex generation [12,13].…”

“…Similar SOI effects involving Bessel beams have been considered in uniaxial crystals [7] and at reflection and transmission by a planar interface between two homogeneous media [8]. The advent of metamaterials has further increased the SOI research effort [9], mostly in the use of ultra-thin metasurfaces for manipulating the angular momentum of light [10,11] and for vortex generation [12,13].Epsilon near zero (ENZ) media are nowadays attracting an increasing research interest due to the very unconventional way they affect the electromagnetic radiation. The effective wavelength in ENZ media is much larger than the vacuum wavelength and this entails a regime quite opposite to geometrical optics where the field is slowly-varying over relatively large portions of the bulk.…”

Tipping solutions: emerging 3D nano-fabrication/ -imaging technologies

“…On the other hand, analogous micro-optical elements can be used to generate 3D structured light carrying a designated spin-AM (SAM) and orbital-AM (OAM), e.g. an optical vortex [4,5]. The 3D shaping of light as well as 3D shaping of matter at the nanoscale is demonstrated using state-of-the-art FIB tools where milling is delivered by Ga, Si, and Au ions with resolution down to 10 nm and aspect ratios of up to 10.…”

Nano-proximity direct ion beam writing

“…The fabricated pattern was consistent all over the structure showing the high temporal beam stability and precise stage positioning. The device has shown superb performance across the entire visible wavelengths range giving high optical vortex purity [44].…”