Chiral Metalens of Circular Polarization Dichroism with Helical Surface Arrays in Mid‐Infrared Region

Abstract

polarization manipulation elements have been the two of the most widely investigated device types because of the essential and indispensable functions of these elements. [5][6][7][8][9] In contrast with the traditional bulky optical lenses, a metalens is a micro/ nanostructured metasurface lens in which the amplitude, phase, and polarization state of the transmitted or reflected electromagnetic waves can be manipulated by the micro/nanostructures at the subwavelength scale based on the effects of surface plasmonic polaritons (SPP) or localized surface plasmonics (LSP), [10][11][12][13][14] Mie resonances, [15] and geometric phase (also known as Pancharatnam-Berry phase, P-B phase), [9,[16][17][18][19][20][21][22][23][24] using which focusing, imaging and/or wavefront manipulation in the transmission or reflection can be achieved. Plasmonic lenses consist of an array of metal plasmonic antennas in which a phase discontinuity related to the geometry and dimension of the metallic antennas appears between the incident electromagnetic wave and the transmitted and/or reflected electromagnetic wave due to the SPP/LSP effects. The ability to generate a spherical wavefront or nondiffracting Bessel beam by an array of gold (Au)_ V-shaped nanoantennas with different geometries and dimensions has been experimentally demonstrated at telecom wavelengths. [13] A dual-polarity metalens consisting of an array of plasmonic dipole antennas on a glass substrate with various orientations has also been experimentally demonstrated, in which a convex or concave lens can be realized with an opposite circular polarized illumination, i.e., either left-handed circular polarization (LCP) or right-handed circular polarization (RCP). [14] Using the similar plasmonic dipoles made of subwavelength metallic nanorods with spatially varying orientations, high-resolution 3D holography can also be achieved. [25] Unlike the plasmonic lens, the all-dielectric metalens based on Mie resonances can also achieve focusing with high efficiency, and a metalens with Si elliptical disks with different dimensions embedded in glass substrate was proposed for this purpose. [15] Recently, the P-B phase has attracted much attention and has been employed in focusing/imaging of the optical metasurface. Unlike the propagation phase, the P-B phase is achieved using azimuth-varied nano/micrograting structures. [26,27] Each nano/microunit (metamolecule) of the metalens is similar to a local half-wave plate (HWP) with different azimuthal angle (θ), so that the circular polarization state of the transmission or reflection is orthogonal to that of the A chiral metalens of circular polarization dichroism (CPD) in the mid-infrared region of 3-5 µm is demonstrated both theoretically and experimentally, in which one of the circularly polarized light beams (either left-handed or righthanded) is transmissively focused at a designed focal length, while the other beam is reflected. The metalens consists of subwavelength helical surface arrays covered by a gold thin film that gives r...

Broadband Design of Midinfrared Chiral Metamaterials Based on the Indium Tin Oxide Conical Helix

“…e regulation of the midinfrared laser polarization state is the key link in midinfrared laser transmission control. As a new type of arti cial electromagnetic material, chiral metamaterials have been widely studied and show strong ability in polarization state regulation [1][2][3][4][5]. Chiral metamaterials introduce chiral structures into metamaterials.…”

Three-dimensional artificial chirality towards low-cost and ultra-sensitive enantioselective sensing

“…Recently proposed advanced materials, 70–72 tunable materials, 73–76 and machine-learning design methods 77–80 empower the development of chiral metamaterials. Furthermore, artificial chiral nanostructures can be utilized in various photonic applications such as chiral metamirrors, 81 metaholograms, 82–86 metalenses, 87,88 multi-mode OAM generators, 89 beam steering, 90 and color prints. 91 These applications can be further improved by analysis of current metasurface and metamaterials that use various optical responses such as Mie-resonance, 92–96 geometric phases, 97,98 nanogap plasmonics, 99,100 nonlinear optics, 101 Bragg-reflection, 102,103 and spin Hall effect.…”

Geometric and physical configurations of meta‐atoms for advanced metasurface holography

“…CMs have distinct complex refractive indices under right‐handed and left‐handed polarized light (Figure 3(A)). 110–113 Such chiroptical property of the CMs imparts spin‐controllable functionality to the geometric metasurfaces 114 . In a chiral meta‐hologram, the Jones matrix is usually defined in circular form as where t ll , t lr , t rl , and t rr are the complex transmittance amplitudes of CMs.…”