Six‐Mode Orbital Angular Momentum Generator Enabled by Helicity‐Assisted Full‐Space Metasurface with Flexible Manipulation of Phase, Polarization, and Spatial Information

Abstract

Vortex beam carrying orbital angular momentum (OAM) has been experiencing a research upsurge attributed to its excellent communication capability, which also boosts the development of the OAM technology and promotes the application of the OAM generator. However, most of the existing designs of the OAM generators can only produce a small number of diverse OAM modes, and restrict the channel capacity of single OAM generator. Herein, an appealing strategy of six‐mode OAM generator based on helicity‐assisted full‐space metasurface is proposed to generate up to six diverse OAM modes by altering the polarization state, illumination region, and incidence direction of incident waves. Significantly, the designed OAM generator has high communication security because of its great information entropy, and the generated OAM modes possess the characteristics of high purity and low crosstalk which result from the orthogonal polarization states and unequal deflection angles of produced vortex beams. A proof‐of‐concept prototype is constructed to corroborate the validity of our methodology, and the results of simulations and experiments are in excellent agreement with theoretical predictions. This fire‐new OAM generator will possess a promising application prospect in communication systems, and may also provide an efficacious method to design multifunctional devices.

Single-Layer Achiral Metasurface with Independent Amplitude–Phase Control for Both Left-Handed and Right-Handed Circular Polarizations

“…Metasurfaces, the artificial planar arrangements of various subwavelength resonators, possess exceptional capability of tailoring the amplitude, phase, and polarization of electromagnetic waves. − Given the merits of low loss, small size, and simple fabrication, metasurfaces have drawn great attention and shown versatile applications, such as vortex beam generators, , focusing lenses, , meta-holograms, − surface plasmon polariton couplers, , etc. − Notably, some efforts are devoted to construction of chiral metasurfaces to acquire desired chiral effects. − For instance, numerous transmission-reflection-selective chiral structures are designed to block one state of the CP waves and transmit orthogonal CP waves. − Some ingenious metasurfaces can achieve circular dichroism by devising the chiral structures or introducing loss resistors into meta-atoms. − Furthermore, a range of schemes are proposed to independently control the wavefronts of LCP waves and RCP waves based on the integrated design of scaling-induced propagation phases and rotation-induced geometric phases. − More strikingly, certain multilayer multifunctional metasurfaces are established to tailor the amplitude and phase of orthogonal CP waves utilizing chiral structures with unequal dimensions working at distinct frequencies. , Nevertheless, most of the existing paradigms increase the complexity of the structures to obtain the intrinsic chirality or combine multilayer achiral structures to get the external chirality, and it is difficult for chiral metasurfaces to manipulate the amplitude and phase of orthogonal CP incident waves independently at the same frequency based on the present design mechanisms. In contrast, there are few studies on chiral phenomena generated by single-layer achiral structures, which means that the immense potential of chiral effects lies in simple achiral structures.…”

Nature engineered metasurfaces: spin-to-orbital angular momentum conversion in diatom frustules

“…OVs can be obtained exploiting phase discontinuities (e.g. by means of spiral phase plates [2], fork holograms [3] or spatial light modulators [4]), inducing spin-to-orbital angular momentum conversion by inhomogeneous birefringent elements (q-plates) [5] or by complex metallic or dielectric metasurfaces [6], or even by photonic crystal slabs supporting bound states in the continuum [7]. Surprisingly, we observed spin-orbit coupling induced by a nanostructured biomaterial.…”

Half‐Integer Topological Charge Polarization of Quasi‐Dirac Bound States in the Continuum

“…However, this analogy is only in the effect of the transformation. In fact, at Vpoints, such conversion is intrinsic in the rotational symmetry of the equifrequency dispersion curve in the momentum space and does not require the inhomogeneous anisotropy in the direct space necessary in q-plates (or in resonance-based metasurfaces with azimuthal space-variant geometry [47][48][49][50][51] ). Thus, the Hopf index TC of the polarization singularity plays the same role of the disclination order q in the inhomogeneous waveplate, TC = q.…”