Huygens Metasurface Research Articles

Enhancing phase modulation and group delay in reflective Huygens metasurfaces via a Fabry-Perot cavity.

Huygens metasurfaces exhibit excellent optical properties such as 2π phase modulation and slow light effects. However, they face challenges including wide bandwidth and low group delay due to their high radiation losses. Here, we propose a reflective Huygens metasurface coupled with an F-P cavity. We demonstrate that F-P resonance modes can couple with magnetic-quasi-bound-state (M-QBIC) and electric-quasi-bound-state (E-QBIC) in the Huygens metasurface through constructive interference, significantly enhancing the quality factors of both QBICs. Through structural parameter optimization, our reflective Huygens metasurface achieves 4π phase modulation and a high group delay of up to 166 ps. Compared to the non-coupled Huygens metasurface with the same structural asymmetry, the group delay of the F-P coupled reflective Huygens metasurface is enhanced by up to 30 times. Our design reduces the fabrication precision requirements for Huygens metasurfaces, enabling similar group delays to be achieved in low-symmetry coupling structures as in highly symmetric non-coupling structures. Additionally, the performance of this metasurface shows robustness to changes in incident light polarization. This design highlights the potential for achieving high-quality factors, large phase modulation, and large group delay, offering new avenues for the design of highly sensitive tunable devices, efficient nonlinear optical devices, and narrowband slow light devices.

Design of reconfigurable Huygens metasurfaces based on Drude-like scatterers operating in the epsilon-negative regime.

In this study, we investigate the feasibility of designing reconfigurable transmitting metasurfaces through the use of Drude-like scatterers with purely electric response. Theoretical and numerical analyses are provided to demonstrate that the response of spherical Drude-like scatterers can be tailored to achieve complete transmission, satisfying a generalized Kerker's condition at half of their plasma frequency. This phenomenon, which arises from the co-excitation of the electric dipole and the electric quadrupole within the scatterer, also exhibits moderate broadband performance. Subsequently, we present the application of these particles as meta-atoms in the design of reconfigurable multipolar Huygens metasurfaces, outlining the technical prerequisites for achieving effective beam-steering capabilities. Finally, we explore a plausible implementation of these low-loss Drude-like scatterers at microwave frequencies using plasma discharges. Our findings propose an alternative avenue for Huygens metasurface designs, distinct from established approaches relying on dipolar meta-atoms or on core-shell geometries. Unlike these conventional methods, our approach fosters seamless integration of reconfigurability strategies in beam-steering devices.

Ultrafast modulable 2DEG Huygens metasurface

Huygens metasurfaces have demonstrated remarkable potential in perfect transmission and precise wavefront modulation through the synergistic integration of electric resonance and magnetic resonance. However, prevailing active or reconfigurable Huygens metasurfaces, based on all-optical systems, encounter formidable challenges associated with the intricate control of bulk dielectric using laser equipment and the presence of residual thermal effects, leading to limitations in continuous modulation speeds. Here, we present an ultrafast electrically driven terahertz Huygens metasurface that comprises an artificial microstructure layer featuring a two-dimensional electron gas (2DEG) provided by an AlGaN/GaN heterojunction, as well as a passive microstructure layer. Through precise manipulation of the carrier concentration within the 2DEG layer, we effectively govern the current distribution on the metasurfaces, inducing variations in electromagnetic resonance modes to modulate terahertz waves. This modulation mechanism achieves high efficiency and contrast for terahertz wave manipulation. Experimental investigations demonstrate continuous modulation capabilities of up to 6 GHz, a modulation efficiency of 90%, a transmission of 91%, and a remarkable relative operating bandwidth of 55.5%. These significant advancements substantially enhance the performance of terahertz metasurface modulators. Importantly, our work not only enables efficient amplitude modulation but also introduces an approach for the development of high-speed and efficient intelligent transmissive metasurfaces.

Huygens’ metasurface: From anomalous refraction to reflection

Huygens' metasurfaces (HMS) without any reflection or transmission are widely studied due to the high-efficiency manipulation of electromagnetic waves. In this work, three-layered metallic Huygens' metasurfaces are proposed and the geometry-dependences of anomalous refraction and reflection are investigated. The surface impedance and admittance are independently tailored by changing the length of metallic resonators, which is dictated by the introduction of the intermediate layer. Huygens’ metasurfaces can be geometrically engineered to realize anomalous refraction with an efficiency of 62% and anomalous reflection with an efficiency of 60%, respectively. It is anticipated that the proposed metasurface with tunable materials could achieve reconfigurable terahertz devices.

Analysis of binary huygens metasurfaces under non-planar illumination

In this article, we have investigated the effect of using a real feed on the performance of one-dimensional binary Huygens metasurfaces (BHMS). The designed structure has variable periods and each unit-cell consists of two dipoles with different lengths. Floquet theory and local constant period assumption are used to design these metasurfaces. The simulation results show the high efficiency of the designed structure and its beam squint capability. The results in this article make it possible to use this type of metasurface in real applications under the illumination of real feed sources.

Multi-feed high-gain Huygens’ metasurface for microwave power transmission

We propose a multi-feed Huygens’ metasurface (HMS) transmitarray designed for microwave power transmission applications. A near-field distributed optimization mechanism is employed to determine the optimal focal lengths of subarrays. We aim to balance between illumination efficiency and interference from incident waves, leveraging the conjugate field matching method for precise phase compensation. This approach ensures robust radiation performance, notably reducing the focus-to-diameter ratio for large-aperture antenna arrays. Consequently, it mitigates spatial dispersion effects and upholds the operational bandwidth of mega antennas. As a proof of concept, we have designed a single-layer HMS transmitarray measuring 1.14 × 1.14 m2 (22 λ at 5.8 GHz). Through simulation, we have attained a peak gain of 35.47 dB and an aperture efficiency of 57.73%. Our design exhibits outstanding radiation performance, combined with advantages, such as a low profile, cost-effectiveness, and scalability.

Anisotropic Bilayer Transmissive Huygens Metasurface for Generating Multi-OAM Beams With Orthogonal Modes and Polarizations

Anisotropic Bilayer Transmissive Huygens Metasurface for Generating Multi-OAM Beams With Orthogonal Modes and Polarizations

Scattered beam control of encoded metasurface based on near-field coupling effects of elements

The coupling effect between the element structures of the traditional Huygens metasurface is easy to cause the efficiency of the designed functional devices to be reduced. In order to eliminate or reduce the coupling effect between the element structures, a border-type Huygens metasurface element structure is proposed. In order to confirm that the bounding element structure can significantly reduce the coupling effect, the near-field distribution and far-field properties of two Huygens metasurfaces with and without bounding are compared. Through comparative analysis, we find that the bounding Huygens element structure can significantly reduce the coupling effect between the element structures, and the far-field scattering angle is more consistent with the theoretical calculation value. In order to realize the free regulation of the far-field scattering angle of THz waves, we introduce the Fourier convolution principle in digital signal processing, and operate the element sequence of Huygens metasurface on the addition principle to realize the free regulation of scattered beams. In addition, we performed functional addition operations on the bounding and unbounding coding sequences. The bounding code structure can accurately achieve the synthesis of functions.

Silicon Rich Nitride Huygens Metasurfaces in the Visible Regime

AbstractIn recent years there has been a shift of interest in the Nanophotonics community moving from using metallic/plasmonic materials to using high‐index dielectric materials for the construction of metasurfaces. Although high‐index dielectrics hold many advantages over their plasmonic counterparts, the selection of materials that exhibit high‐index properties, have low loss, and are complemetary metal‐oxide‐semiconductor (CMOS) compatible that also operate in the visible regime is extremely challenging. In this work, a high‐index dielectric material using silicon rich nitride (SRN) is proposed and experimentally demonstrated as a platform for solving this problem. While SRN has been used before for diffractive lenses and structural colors, here its applicability for Huygens‐type metasurfaces is focused upon. Specifically, a Huygens metasurface that operates in the visible range around a wavelength of 575 nm is theoretically and experimentally demonstrated, and the capabilities of spatially controlling the phase of this metasurface are further demonstrated by designing and fabricating a Huygens meta hologram. The study also shows that the refractive index can be controlled by the interplay between SiH4 and NH3 during the plasma‐enhanced chemical vapor deposition (PECVD) process.

Continuously Tunable Optical Modulation Using Vanadium Dioxide Huygens Metasurfaces.

Efficient and dynamic light manipulation at small scale is highly desirable for many photonics applications. Active optical metasurfaces represent a useful way of achieving this due to their creative design potential, compact footprint, and low power consumption, paving the way toward the realization of chip-scale photonic devices with tunable optical functionality on demand. Here, we demonstrate a dynamically tunable, dual-function metasurface based on dielectric resonances in vanadium dioxide that is capable of independent active amplitude and phase control without the use of mechanical parts. Significant developments in the nanofabrication of vanadium dioxide have been shown to enable this metasurface. Gradual thermal control of the metasurface yields a computationally predicted continuously tuned amplitude modulation of 19 dB with negligible phase modulation and a continuously tuned phase modulation of 228° with negligible amplitude modulation, both at near-infrared wavelengths. Experimentally, a maximum continuously tuned amplitude modulation of 9.6 dB and phase modulation of 120° are shown, along with demonstration of stable intermediate states and repeated modulation without degradation. Reprogrammable optical functionality can thus be achieved in precisely engineered nanoantenna arrays for adaptive modulation of amplitude and phase of light for applications such as tunable holograms, lenses, and beam deflectors.

Simple and Comprehensive Strategy to Synthesize Huygens Metasurface Antenna and Verification

Huygens metasurface (HMS) provides a flexible way to tailor the phases of fields without incurring reflection. Recently, HMS has been used in antenna scenes to convert the incident field into directional radiation. However, most design processes of the HMS antennas are based on the generalized sheet transition condition, which is usually augmented with extra operations for ensuring passivity and losslessness. Here, we propose a simple and comprehensive strategy to design and optimize the HMS antenna. The strategy builds an equivalent model of the HMS antenna and deals with the designs from the perspective of phase optimization, which is simple and straightforward. A fast and efficient algorithm is presented to solve the optimization problem under the framework of alternating direction method of multipliers (ADMM). The phases obtained by this strategy are naturally compatible with the passive and lossless conditions and can be directly implemented by metasurfaces. Furthermore, the strategy imposes constraints on the phase difference of adjacent meta-atoms, thus reducing the performance deterioration caused by aperiodic boundary conditions. The feasibility and superiority of the strategy are verified by full-wave simulation results and experimental measurements of exemplary designs.

Wideband Transmit-Array Antenna Design With Dual-Layer Ultrathin Huygens’ Meta-Surface for Vehicular Sensing and Communication

This paper proposes a wideband high-gain transmit-array (TA) antenna for vehicular sensing and communication, which employs a dual-layer ultrathin Huygens' meta-surface (HMS). It consists of a 33 × 33 HMS unit cells-based TA, a feeder horn, and a three-dimensional printed fixture to hold them. Each HMS unit cell has two identical metal patterns (MPs) of two symmetrical U-shaped patches and one H-shaped patch, which are distributed on both surfaces of the ultrathin substrate. A pair of top U-shaped patches form the first single-wavelength loop mode, and another pair of bottom U-shaped patches forms the second single-wavelength loop mode. Due to the different phases of the incident waves on the top and bottom U-shaped patches, the two loop modes are generated at different frequencies. A third half-wavelength dipole mode is provided by the H-shaped patch. The three modes correspond to three different frequencies, forming a wide transmission frequency band. Three near-unity transmission peaks are yielded to ensure high and stable aperture efficiency (AE). As well, the transmission phase of the HMS unit cell varies with geometric dimensions, and five unit cell types are quantized to obtain 360° phase range with a low loss of less than 2.6 dB. To verify the design concept, a prototype is fabricated. Measurements show a 3-dB gain bandwidth of 17.9%, a maximum gain of 30.5 dBi at 26.2 GHz, and a high AE of 41.9%. It has unidirectional radiation pattern while reducing backlobe.

A Double-Layer Dual-Polarized Huygens Metasurface and Its Meta-Lens Antenna Applications.

In this paper, a dual-polarized Huygens unit is proposed, which has a double-layer metallic pattern etched on both sides of one dielectric substrate. Induced magnetism enables the structure to support Huygens' resonance, thus obtaining nearly complete available transmission phase coverage. By optimizing the structural parameters, a better transmission performance can be achieved. When the Huygens metasurface was used for the design of a meta-lens, good radiation performance was exhibited, with a maximum gain of 31.15 dBi at 28 GHz, an aperture efficiency of 42.7% and a 3 dB gain bandwidth of 26.4 GHz to 30 GHz (12.86%). Due to its excellent radiation performance and very simple fabrication, this Huygens meta-lens has important applications in millimeter-wave communication systems.

A W-Band High-Gain Bilayer Transmit-Array Antenna Employing Huygens’ Resonance

A special type of transmissive phase plate, named Huygens' metasurfaces (HMS), is capable of efficiently manipulating transmitted electromagnetic wavefronts with extremely low back-scattering. Here, in contrast to conventional planar multilayer lens arrays, a transmit-array (TA) antenna based on Huygens' resonance is proposed for high-gain applications at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band. The proposed meta-cell is comprised of a pair of parallel metallic strips on opposite sides of a single dielectric substrate connected by a pair of vias, and can independently control the electric and magnetic dipole responses and induce the desired Huygens' resonance. An equivalent circuit model (ECM) is used to describe its operation principle in detail. A full 360 degrees phase coverage and a high transmission amplitude can be obtained simultaneously using the proposed unit cell. To experimentally verify the proposed concept and design, a TA antenna is fabricated and tested. The Huygens' TA prototype exhibits good radiation performance. The measured peak gain of the TA prototype is 34.341 dBi at 87 GHz with an aperture efficiency of 45.7%, and the measured 3-dB gain bandwidth is from 79 to 90 GHz.

Study of Parallel-Plate Waveguides Bordered by Reactive Huygens Metasurfaces

Huygens metasurfaces (HMSs) are 2-D structures exhibiting both electric and magnetic responses. In this article, the properties of a parallel-plate waveguide (PPW) formed by two dispersive reactive HMSs are investigated analytically by deriving the dispersion relations for supported surface waves. In particular, the PPWs formed by nondispersive HMSs are studied thoroughly and it is shown that they can support a maximum of four modes with a variety of transverse electric (TE) and transverse magnetic (TM) degenerate modes, modes with the same cutoff frequencies, and modes with constant phase and group velocities. Such explored PPWs offer degenerate modes with orthogonal polarizations with potential applications in leaky wave antennas and holographs. Moreover, PPWs with either nondispersive or dispersive borders support modes with subluminal phase velocities which find applications in device miniaturization. The proposed analytical derivations are verified by full-wave numerical simulations.

Uniform Huygens Metasurfaces with Postfabrication Phase Pattern Recording Functionality

With the rapid progress in the field of metasurfaces and their use in miniature integrated devices arises the quest for cheap mass production of efficient metasurfaces. We suggest a novel way to design and fabricate phase-gradient Huygens metasurfaces using laser-annealing of uniform particles made of As2S3 chalcogenide glass. We show that a phase gradient metasurface can be realized by tuning the refractive index of otherwise identical meta-atoms instead of tuning their geometry. We are using an array of identical As2S3 particles with the possibility to locally change their refractive index using a short-wavelength illumination (green laser) in order to tune the phase pattern at the postfabrication stage. Metasurfaces fabricated with this method can be used for operation in the red or IR spectral range. We fabricate uniform As2S3 Huygens metasurfaces using electron beam lithography and demonstrate their postfabrication tuning with exposure of comparatively low intensity. Sample characterizations with transmittance measurements and quantitative phase microscopy provide results in good correspondence with numerical predictions confirming postfabrication spectral tuning. Using such tuning, we demonstrate the possibility of transferring the intensity pattern produced by modifying a writing beam with a spatial light modulator to a phase pattern recorded on a uniform As2S3 metasurface. Our method has potential advantages for the low-cost production of large-scale metasurfaces because uniform geometries are better adjusted for mass manufacturing.

Switchable Unidirectional Radiation from Huygens Dipole Formed at an Exceptional Point in Non-Hermitian Plasmonic Systems

Non-Hermitian (NH) photonics has attracted considerable attention from researchers owing to exotic properties that originate from the parity–time (PT) phase transition and exceptional points (EPs). In this work, we propose and numerically demonstrate formation of a Huygens dipole using an EP eigenstate in NH coupled plasmonic systems. Unidirectional radiation from the artificial Huygens dipole can be switched via the sign of a coupling constant. In our systems, the formation of the Huygens dipole and its switchable unidirectional radiation are manifested as long as the EP condition is fulfilled. The presented method to control artificial electric and magnetic dipoles based on NH systems would provide new roots to construct Huygens metasurfaces and Huygens dipole antennas.

Transmission Gratings relying on Huygens Metasurfaces for short-wave to long-wave infrared applications

In many spectroscopic applications, diffraction gratings are the pivotal optical component which is used to decompose white light into its spectrum. However, design and manufacturing of diffraction gratings for the infrared spectral domain operating in transmission bares its own challenges, i.e. a very limited choice of transparent materials. Here we present our effort on exploiting Huygens-metasurface structures for design and manufacturing of diffraction gratings intended for operation in the short-wave (around 2µm) up to the long-wave infrared region (&gt;10µm). Silicon nano-pillars are the material system of choice since they exhibit the best compromise between optical performance and manufacturing feasibility. We present specific designs as well as measurement results of a demonstrator sample.

Dynamic Transmissive Metasurface for Broadband Phase‐Only Modulation Based on Phase‐Change Materials

AbstractDynamic metasurfaces provide exciting opportunities for spatial light modulation with ultra‐compact footprint and high resolution. Designs reported so far typically suffer from efficiency problem due to the strong coupling between amplitude and phase modulation. Huygens metasurface design eliminates the back propagation with interference of dual resonances, offering a potential solution for phase‐only modulation. However, the intrinsic dispersion mismatch between the dual modes restricts this design to a highly limited bandwidth. Here, a dynamic phase‐change metasurface design that enables transmissive phase modulation covering over 240° with high‐level transmisstance maintained over 0.8 and a large operation bandwidth of 80 nm ranging from 1516 to 1596 nm, is presented. To verify the potential usage of this design, a multi‐state phase‐change control scheme that enables quasi‐continuous phase modulation is further provided. The key feature of this design is the leverage of congener Huygens concept. Judicious incorporation of lossless phase‐change material (PCM) with congener Huygens metasurface allows wideband holding of Huygens condition, which provides a perfect platform to simultaneously address the efficiency and bandwidth problems. This novel feature represents a meaningful step forward to integrate spatial light modulation.

Static and Reconfigurable Huygens’ Metasurfaces: Use in Antenna Beamforming and Beam Steering

In this article, we review recent advances in static and reconfigurable Huygens’ metasurfaces (HMSs) for antenna beamforming and beam steering. First, the fundamental theory of HMSs is summarized along with basic approaches for their physical realization. Subsequently, precise antenna beamforming without feeding networks by utilizing static HMSs is described. This is followed by the description of using HMSs as radomes for extending the scan range of phased arrays. Finally, several strategies are described for realizing reconfigurable HMS by means of electronic control devices.