Polarization-Engineered Noninterleaved Metasurface for Integer and Fractional Orbital Angular Momentum Multiplexing

Traditional methods of generating vortex beams based on metasurfaces consist mainly in modulating propagation phase or geometric phase. Here, by introducing detour phase, we propose the construction of dual-polarized vortex beam generators in the form of metasurface and metagrating (MG). The phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells. To use detour phase, two kinds of unit cells are designed to achieve specific diffraction order. Each unit can arbitrarily and independently adjust the operation frequency and diffraction angle of transverse electric (TE) and transverse magnetic (TM) polarizations. Two vortex beam generators are designed and fabricated with different topological charges carried by orthogonal polarizations. To demonstrate the ability to independently manipulate, two polarizations of the generator based on MG are designed in different frequency bands. Both the simulation and experimental results validate the proposed method, showing great potential for polarization division multiplexing in orbital angular momentum (OAM) communication systems. 

Generating Dual-Polarized Vortex Beam by Detour Phase: From Phase Gradient Metasurfaces to Metagratings

Symmetric spin–orbit interaction (SOI)‐based approaches apply a practical limit on helicity multiplexed metaoptics, i.e., center symmetric information encoding. Contrarily, asymmetric SOI's based on the combination of geometric and propagation phase‐delay approaches can effectively address such limitations for multifunctional multiplexed metaoptics on the cost of design complexities. In this paper, a simple asymmetric SOI‐based technique is realized for multifunctional metaoptics, employing only a single unit cell, breaking the conventional tradeoff between design complexity and efficient asymmetric transmission efficiency. The design approach depends on geometric phase alone, which eases the fabrication challenges and decreases the computational cost associated with previous asymmetric SOI‐based metaoptics. Furthermore, this study utilizes a new, low‐cost CMOS‐compatible material to optimize the proposed single unit cell for low loss and high transmission efficiency over the complete visible domain. On‐axis and off‐axis holographic metasurfaces are designed and integrated with pressure‐sensitive liquid crystal cells to demonstrate actively tunable metaholography with no limitation of center symmetric information encoding. The simple design technique, cost‐effective fabrication, and finger touch‐enabled holographic output switching make this integrated setup a potential candidate for many applications such as smart safety labeling, motion or touch recognition, and interactive displays for impact monitoring of precious artworks and products.

Novel Spin‐Decoupling Strategy in Liquid Crystal‐Integrated Metasurfaces for Interactive Metadisplays

There is a huge demand to accurately determine the magneto-electrical properties of particles in the nano sized regime due to the modern IC technology revolution and biomedical application science. In this paper, we present a microwave waveguide measurement technique for complex permeability and permittivity of expensive nano sized magnetic powder materials. In the measurement process, Agilents 8510C vector network analyzer was used to have a standard TRL calibration for free space inside the waveguides. In order to maintain the recommended insertion phase range, a very thin prepared sample was loaded inside the calibrated waveguide. Also, the loaded materials magnetic and dielectric effects were considered into the cutoff wavelength of the propagation constant of the TE10 wave from the geometrical dimensions of the waveguides. This makes the measured permeability and permittivity more reliable than commonly used techniques. The six different compounds of nano sized ferrite powders (Fe3O4, CuFe2O4, CuFe2O4Zn, Fe2NiO3Zn, BaFe12O19, and SrFe12O19), in which the average diameter of nano particles is less than 40nm were purchased from Sigma-Aldrich, Inc for measurement purposes employing this technique. For industrial benefits, we present the complex permeability and permittivity on the frequency range from 3.95GHz to 5.85GHz. The measured results showed that the dielectric permittivity of these materials is quite different from those of solid state materials. Index Terms, Nano ferrites, waveguide technique, permeability, permittivity.

Nano Ferrites Microwave Complex Permeability and Permittivity Measurements by T/R Technique in Waveguide

Resonant metasurface (MTS) antennas (RMAs) are antennas leveraging unusual standing-wave modes of truncated MTS. By introducing resonant exciters, such as wire (electric currents), aperture (magnetic currents), or both, the antenna bandwidth can be improved. However, the contributing modes of apertures are not well recognized. A systematic framework is formulated for the characteristic mode analysis (CMA) and design of RMAs involving resonant apertures, by designing a low-profile wideband dual-polarized RMAs fed by slot arrays at 5 GHz Wi-Fi bands. Unlike regular microstrip patches, the aperture-backed MTS supports two fundamental TM03 modes of different symmetries. Even and odd symmetries are also observed for the aperture modes. By calculating the radiating power of individual mode, quantitative evidence is provided to clarify the operating principle of RMAs with resonant apertures that the bandwidth improvement and high-isolations are due to the modes from both the MTS and the aperture, rather than from individual. The overall size of the proposed antenna is $\lambda _{\mathrm {L}} \times \lambda _{\mathrm {L}} \times 0.058\lambda _{\mathrm {L}}$ ( $\lambda _{\mathrm {L}}$ is the free-space wavelength at 4.8 GHz). The measured bandwidth is 25% (4.8–6.2 GHz) with $\vert S_{11}\vert dB, $\vert S_{21}\vert dB, boresight gain of 8–10 dBi and cross-polarization level better than −28 dB.

Resonant Metasurface Antennas With Resonant Apertures: Characteristic Mode Analysis and Dual-Polarized Broadband Low-Profile Design

Vortex beams have witnessed tremendous development in the past
decade by exhibiting profound implications for both fundamental physics
and a multitude of novel engineering applications. In this work, broadband
high-efficiency multiple vortex beams with independent topological modes
and inclination angles are generated leveraging an interleaved
geometric-phase multifunctional metasurface operating in a very broadband
frequency range. A set of meta-atoms are elaborately engineered to offer
broadband high-efficiency complete phase control covering the entire
2π range. Multiple geometric-phase sub-arrays implemented by the
designed meta-atoms are synthesized into one metasurface via a
shared-aperture interleaved manner, in which each sub-array can be
individually manipulated and serves as an independent channel for
launching a vortex beam. According to the established design methodology,
two vortex beams with topological modes of −1 and +2 and
distinct inclination angles are generated by one metasurface. Experimental
results are provided to corroborate the proposed mechanism for multiple
vortex beams generation, which exhibit broadband and high-efficiency
features. The presented multifunctional metasurface paves the way for the
generation of broadband high-efficiency multiple vortex beams in the
microwave, millimeter-wave and terahertz regions. This work is of
significance for high-capacity wireless communication applications,
high-efficiency manipulation of electromagnetic waves, and novel design of
radar and imaging systems.

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

Enhanced Sub-Terahertz Microscopy based on Broadband Airy Beam

The electromagnetic scattering of an object is directly related to its physical geometry and material properties. While metasurfaces show excellent performances in mimicking material properties almost at well by flexibly designing meta‐atoms with arbitrary electromagnetic responses, their physical geometries are generally in a regular manner. The break of a metasurface's geometry will inevitably affect its electromagnetic scattering that introduces uncertainty in wavefront manipulation. Here, a general approach for highly efficient wavefront manipulation with irregular shaped metasurfaces is proposed. Such an approach establishes a universal iterative modulation relation between the metasurface and scattered field by introducing boundary constraints at the aperture, enabling to deal with the electromagnetic scattering from a metasurface with arbitrary spatial shape. In this way, the desired wavefront form can be engineered using meta‐atom sequences with arbitrarily shaped aperture. As a proof of concept, a flower‐shaped metasurface operating in the reflection mode is designed and experimentally demonstrated for reconstructing four random focuses with uniform and high‐efficiency intensity distribution at near‐field region, while the flower shaped field pattern can be extracted near the aperture plane. Such a method may pave a new route for advanced wavefront manipulation and electromagnetic concealment/camouflage applications.

Shaping Electromagnetic Fields with Irregular Metasurface

Polarization-Assisted Visual Secret Sharing Encryption in Metasurface Hologram

Abstract Electromagnetic vortex carries the orbital angular momentum, one of the most fundamental properties of waves. The order of such vortex can be unbounded in principle, thus facilitating high-capability wave technologies for optical communications, photonic integrated circuits and others. However, it remains a key challenge to generate the high-order vortex beams in a reconfigurable, broadband and cost-effective manner. Here, inspired by the balanced-ternary concept, we demonstrate the reconfigurable generation of order-controllable vortices via cascaded N-layer metasurfaces. We theoretically showed that 3 N − 1 ${3}^{N}-1$ different vortex modes can be generated by cascading N metasurfaces, each one serving as an individual vortex beam generator for the order of 3 k ${3}^{k}$ (k = 0,1,2 …, N − 1 $N-1$ ). As a proof-of-concept demonstration, a reconfigurable generation of 26 different vortex beams, with orders from 1 to 13 and from −1 to −13, is showcased in a broad millimeter-wave region by a cascade of 3 metasurfaces. Our method can be easily extended to vortex beam generator of arbitrary orders in a reconfigurable and easily implementable manner, paving a new avenue towards tremendous practical applications.

/pdf/balanced-ternary-inspired-reconfigurable-vortex-beams-using-2ruucezl.pdf

Ji Liu

Papers

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

Enhanced Sub-Terahertz Microscopy based on Broadband Airy Beam

Shaping Electromagnetic Fields with Irregular Metasurface

Polarization-Assisted Visual Secret Sharing Encryption in Metasurface Hologram

Balanced-ternary-inspired reconfigurable vortex beams using cascaded metasurfaces