Transverse Electric Waves Research Articles

ITO-Based Electrically Tunable Metasurface for Active Control of Light Transmission.

In recent years, the rapid development of dynamically tunable metasurfaces has provided a new avenue for flexible control of optical properties. This paper introduces a transmission-type electrically tunable metasurface, employing a series of subwavelength-scale silicon (Si) nanoring structures with an intermediate layer of Al2O3-ITO-Al2O3. This design allows the metasurface to induce strong Mie resonance when transverse electric (TE) waves are normally incident. When a bias voltage is applied, the interaction between light and matter is enhanced due to the formation of an electron accumulation layer at the ITO-Al2O3 interface, thereby altering the resonance characteristics of the metasurface. This design not only avoids the absorption loss of metal nanostructures and has a large modulation depth, but also shows compatibility with complementary metal oxide semiconductor (CMOS) technology.

Strong and wide-angle nonreciprocal radiation in modified distributed Bragg reflector-Weyl semimetal heterostructure

An approach to obtain easy-to-fabricate and spectrally selective nonreciprocal thermal emitter (NTE) has been proposed. The presented hybrid structure is composed of Weyl semimetal (WSM) film sandwiched by Ge/BaF2/Ge tri-layer and metal substrate. It has been shown that structural parameters hold tolerance on the order of hundreds of nanometers, which are highly favorable for fabricating with low cost and high performance. Multiband responses of the device can be realized through controlling the thickness of last Ge layer, which boosts the flexibility of preparation and potential applications. The giant nonreciprocity can be maintained with broad polar and azimuthal angle ranges. By manipulating the structural parameters, a remarkable result of nonreciprocal radiation is realized under both the transverse electric (TE) and transverse magnetic (TM) wave incidence. By changing the azimuthal angle (ϕi) of incidence, the nonreciprocity (η) can be effectively manipulated. The simulated η spectra is symmetric along the azimuthal angle ϕi=90°, and η=0 when ϕi=90°. Our results provide a much simpler way to achieve the multi-channel nonreciprocity and could lead to the advancement of power scavenging and conversion devices.

Investigation on mechanical properties and stealth characteristics of a novel gradient-stitched composite structure

Based on the far field function of electric field, a new glass carbon fiber gradient-stitched structure is proposed and designed in the paper. In the frequency range of 8–28 GHz, the electric field distribution of transverse electric and magnetic field (TEM) waves incident obliquely on the surface of the structure by optimizing the glass fiber fabric units. It is confirmed that the surface has the function of suppressing electromagnetic wave reflection. The electrical performance simulation and testing results of the structure show that the radar cross section (RCS) is reduced by 90% in the frequency range of 12.3–26.5 GHz. In addition, a multi-scale analysis model is established to quickly predict the tensile modulus and strength of the composite material. The strength and modulus reached 26.9 GPa and 403 MPa, respectively. The simulating and testing results of mechanical properties are in good agreement.

Hybridization of the A- and B-Exciton in a WS2 Monolayer Mediated by the Transverse Electric Polarized Wave Supported by a Si3N4/Ag Heterostructure

Hybridization of the A- and B-Exciton in a WS₂ Monolayer Mediated by the Transverse Electric Polarized Wave Supported by a Si₃N₄/Ag Heterostructure

A Convolutional Neural Network with Multifrequency and Structural Similarity Loss Functions for Electromagnetic Imaging.

In this paper, artificial intelligence (AI) technology is applied to the electromagnetic imaging of anisotropic objects. Advances in magnetic anomaly sensing systems and electromagnetic imaging use electromagnetic principles to detect and characterize subsurface or hidden objects. We use measured multifrequency scattered fields to calculate the initial dielectric constant distribution of anisotropic objects through the backpropagation scheme (BPS). Later, the estimated multifrequency permittivity distribution is input to a convolutional neural network (CNN) for the adaptive moment estimation (ADAM) method to reconstruct a more accurate image. In the meantime, we also improve the definition of loss function in the CNN. Numerical results show that the improved loss function unifying the structural similarity index measure (SSIM) and root mean square error (RMSE) can effectively enhance image quality. In our simulation environment, noise interference is considered for both TE (transverse electric) and TM (transverse magnetic) waves to reconstruct anisotropic scatterers. Lastly, we conclude that multifrequency reconstructions are more stable and precise than single-frequency reconstructions.

Based on the preparation of dual-absorber agents using Ni and Ni/rGO for the fabrication of a dual honeycomb nested structure for wideband microwave absorption

Designing absorbers with structural support to achieve ultra-wideband and wide-angle absorption properties is crucial for addressing the growing concern of electromagnetic pollution. In this study, a strategy is proposed to further broaden the bandwidth of structural absorbers by applying different materials to different structures and then nesting these different structures. Six composite materials were prepared using Ni and rGO as absorbers, and a dual honeycomb nested structure was fabricated using 3D printing technology. The minimum reflection loss (RL) of the two types of composite materials was −19.3 dB and −15.8 dB, respectively, with effective absorption bandwidths (EAB) of 4.6 GHz and 4.4 GHz, demonstrating mechanical compatibility and electromagnetic substitutability. The dual honeycomb nested structure utilized a multiscale design approach, achieving broadband absorption up to 14.27 GHz and compressive strength of 5.92 MPa. Furthermore, stable frequency response of transverse electric (TE) waves was observed within an incident angle range of 0°–40°, while absorption frequencies exceeded 12 GHz as transverse magnetic (TM) waves incident angle varied from 0° to 60°, highlighting wide-angle absorption characteristics. The dual composite preparation strategy of materials and structures for absorber fabrication provides a new perspective for further expanding the bandwidth of absorbers.

Linearly polarized GaN micro-LED with adjustable directional emission integrated with a continuous metasurface

Traditional LEDs emit light that exhibits incoherence and displays a Lambertian distribution. To achieve linearly polarized (LP) light and control the emission direction, a variety of optical components are required to be stacked, which is unsuitable for compact applications and results in low deflection efficiency. Here, we propose and and numerically simulate a novel single-chip micro-resonant cavity LED (micro-RCLED) device that generates directional LP light by integrating a continuous metasurface. This device includes a bilayer grating at the GaN layer's bottom, providing high transverse electric (TE) reflectivity above 89.5% and an extinction ratio exceeds 57 dB at 500 nm. The top distributed Bragg reflector (DBR) and the bilayer grating together constitute a TE mode Fabry–Pérot resonant cavity. This not only promotes the emission of the TE wave, but also guarantees its collimation with the appropriate phase, thereby enhancing its spatial coherence. A functional metasurface above the DBR layer precisely controls the TE wave's deflection angle. It maintains a low aspect ratio while enabling efficient, large-angle deflection. The simulation results demonstrate that this device provides an effective solution for generating highly spatially coherent directional LP light, with broad potential applications in fields such as polarized light imaging and advanced 3D micro-LED display systems.

Strain-Induced Electromagnetic Transmission Modulation via a Reconfigurable Kirigami Metasurface

Tunable three-dimensional (3D) electromagnetic (EM) metasurfaces are critical for dynamic modulation of EM responses but their construction and tuning mechanism are still complex. Here, we report a simple yet effective 3D reconfigurable EM metasurface, which was obtained from a planar kirigami polyimide substrate printed with periodically arranged copper split-ring resonator. Under mechanical stretch, the two-dimensional (2D) planar metasurface can be uniformly deformed into a 3D state, which is effective for tuning its EM transmission characteristic. By combining mechanics and EM simulations as well as experimental measurements, we revealed the deformation mode and active EM transmission modulation capability of the metasurface. It is shown that at the initial state, the planar kirigami metasurface exhibits ideal frequency selective transmission to transverse electric (TE) wave but allows for complete transmission for transverse magnetic (TM) wave. As the applied strain increases from 0% to 20%, the transmission was adjusted from −17.74[Formula: see text]dB to −9.74[Formula: see text]dB for TE wave but merely from 0[Formula: see text]dB to −3.25[Formula: see text]dB for TM wave. Meanwhile, the resonant frequency experienced a visible shift for both TE and TM waves. Finally, the equivalent circuit analysis and simulated surface current density were conducted to reveal the tuning mechanism of the proposed metasurface.

Mechanical and optical properties of porous black Al2O3: Experimental, DFT, and wave optics investigation

Porous black Al2O3 was fabricated by gel casting and pressureless sintering (PS). MnO2 and Fe2O3 incorporated in Al2O3 led to the formation of MnAl2O4 and FeAl2O4 at ≥1200 °C, enhancing its opacity. The influence of various MnO2 content and sintering temperature on the mechanical and optical properties of porous black Al2O3 was investigated. The results showed that as MnO2 content and sintering temperature increased, porosity decreased, bulk density increased, compressive strength increased, and opacity increased. Using density functional theory (DFT), the intrinsic properties of MnAl2O4 and FeAl2O4 were investigated, including band structure (BS), electron distribution, partial density of states (PDOS), and optical properties such as refractivity, absorption, dielectric constant, conductivity, and dissipation factor across various wavelengths. These DFT calculations were incorporated into the wave optics model to assess the response and impedance matching of porous black Al2O3 to transverse electric (TE) and transverse magnetic (TM) waves with various MnAl2O4 content.

Tamm phonon-polaritons triggered in hyperbolic material hexagonal boron nitride

Tamm phonon polaritons (TPhPs) have been recently predicted and experimentally observed for the first time in silicon carbide (SiC) film, allowing for enhanced light–matter interactions and new opportunities for manipulating light at the micro- and nano-scale. Hyperbolic material hexagonal boron nitride (hBN), a two-dimensional Van der Waals crystal, also supports phonon polaritons. However, TPhPs in hBN have not been systematically studied yet. In this paper, we theoretically investigate TPhPs triggered in the structure based on one-dimensional photonic crystal (PC) and hyperbolic material hBN film. It is found that the structure PC/spacer/semi-infinite hBN film can form TPhPs in the Type-II hyperbolic band, but not in the Type-I hyperbolic band. This phenomenon of selective excitation is attributed to the negative permittivity of hBN in the plane, rather than its out-of-plane permittivity. Importantly, TPhPs are sensitive to the thickness of the spacer, which can be regulated flexibly by changing the thickness. In addition, the selective excitation of TPhPs for hyperbolic bands in the configuration of finite hBN/spacer/PC is demonstrated using the same approach. It can be found that the absorption can reach 0.9 at the wavelength of 7.23 μm regardless of transverse electric or transverse magnetic waves, and the observed resonance has high quality factor of 181. This work provides a theoretical basis for TPhPs based on hyperbolic materials and has potential applications in highly sensitive sensors and selective absorbers.

Terahertz Polarization Isolator Using Two-Dimensional Square Lattice Tellurium Rod Array.

A novel terahertz polarization isolator using a two-dimensional square lattice tellurium rod array is numerically investigated at the interesting band of 0.22 THz in this short paper. The isolator is designed by inserting six hexagonal tellurium rods into a fully polarized photonic crystals waveguide with high efficiency of -0.34 dB. The TE and TM photonic band gaps of the 7 × 16 tellurium photonic crystals are computed based on the plane wave expansion method, which happen to coincide at the normalized frequency domain from 0.3859(a/λ) to 0.4033(a/λ), corresponding to the frequency domain from 0.2152 to 0.2249 THz. The operating bandwidth of the tellurium photonic crystals waveguide covers 0.2146 to 0.2247 THz, calculated by the finite element method. The six hexagonal tellurium rods with smaller circumradii of 0.16a serve to isolate transverse electric waves and turn a blind eye to transverse magnetic waves. The polarization isolation function and external characteristic curves of the envisaged structure are numerically simulated, which achieves the highest isolation of -33.49 dB at the central frequency of 0.2104 THz and the maximum reflection efficiency of 98.95 percent at the frequency of 0.2141 THz. The designed isolator with a unique function and high performance provides a promising approach for implementing fully polarized THz devices for future 6G communication systems.

Multi-functional and actively tunable terahertz metamaterial absorber based on graphene and vanadium dioxide composite structure

In this paper, a fabrication friendly terahertz (THz) metamaterial hybrid absorber comprised of square-shaped graphene and U-shaped vanadium dioxide is proposed and numerically analyzed. This device can be tuned dynamically to function as a wide-broadband, reduced-broadband, multi-band, or perfect single-band absorber. Switchable qualities are achieved through simultaneous tuning of the electrical properties of graphene and the phase transition properties of vanadium dioxide. The theory behind the absorption is explored using the distribution of the electric field and the theory of impedance matching. It is clear from the simulation results that the suggested structure can perform as a wide-broadband absorber for the transverse electric (TE) wave during the insulating phase of vanadium dioxide. In this case, graphene’s Fermi energy is configured to 0.7 eV, and it has a 0.1 ps relaxation time. Moreover, only changing the relaxation time to 0.5 ps enables the identical structure to perform as a multi-band absorber. On the contrary, the designed structure exhibits a reduced broadband absorption for the TE wave when the vanadium dioxide is thermally tuned to a metallic state and graphene’s Fermi energy is configured to 0 eV with a 0.1 ps relaxation time. Moreover, by inducing the metallic state in vanadium dioxide and adjusting the Fermi energy of graphene to 0.3 eV with a 0.1 ps relaxation time, the structure performs as a single-band perfect absorber. The main advantage of this work is that the proposed absorber device can be operated as a single-band, multi-band, or broadband absorber with two different bandwidths by applying external voltage and changing temperature. Additionally, for both the TE and transverse magnetic (TM) waves, the structure retains a high level of absorption until 40° of incident angle. Finally, due to its multi-functional property, simple geometric structure, and actively adjustable function, the presented structure has possible real-life applications in the terahertz frequency range.

Near‐Field Coupling of Janus Dipoles Beyond Polarization Locking

AbstractPolarization, as a fundamental property of light, plays a key role in many phenomena of near‐field coupling, namely the coupling of source's evanescent waves into some guided modes. As a typical example of the polarization‐locked phenomenon in the near‐field coupling, the Janus dipole has the orientation of its near‐field coupling face intrinsically determined by the polarization state of linearly‐polarized surface waves, specifically whether they are transverse‐magnetic (TM) or transverse‐electric (TE) surface waves. Here, a mechanism to achieve the directional near‐field coupling of Janus dipoles beyond polarization locking by leveraging hybrid TM‐TE surface waves is presented. These hybrid surface waves, as eigenmodes with both TM and TE wave components, can be supported by optical interfaces between different filling materials inside a parallel‐plate waveguide. Under the excitation of hybrid surface waves, it is found that the coupling and non‐coupling face of a Janus dipole may be switched, if the Janus dipole itself rotates in a plane parallel to the designed optical interface between different filling materials, without resorting to the change of surface‐wave polarization. The underlying mechanism is due to the capability of hybrid surface waves to extract both the source's TM and TE evanescent waves, which offers an alternative paradigm to regulate the interference in the near‐field coupling.

Silicon-based ultra-broadband mid-IR and LWIR near-perfect metamaterial absorber

Ultra-broadband metamaterial absorbers (UBMAs) that are compatible with CMOS technology for use in the mid-infrared and long-wave infrared regions are crucial for a variety of applications, including radiative cooling, thermal photovoltaic, and thermal imaging. In this regard, we propose, in this work, a design of an UBMA based on the heavily doped silicon (D-Si) and silicon carbide (SiC). The 3D finite-difference time-domain method is used, mainly, to numerically calculate the optical characteristics of the proposed UBMA. The absorber, which is made up of a periodic array of symmetrical multilayered square rings of D-Si and SiC, achieves high absorption with an average absorption of 95% over a wavelength range of 2.5–22 µm. This broad range of wavelength absorption is attained, encompassing the mid-, long-wave, and partial far-infrared regions. In addition to the materials' inherent absorption, the stimulation of magnetic polaritons, surface plasmon polaritons, localized surface plasmon resonance, and cavity resonance are responsible for the nearly perfect broadband absorption. Under normal incidence, the proposed UBMA is polarization-independent due to the symmetrical design of the absorber. Furthermore, the impact of the incidence angle on the absorption of transverse electric and transverse magnetic waves is examined.

High-Frequency Hall Effect and Transverse Electric Galvanomagnetic Waves in Current-Biased 2D Electron Systems

We derive the electrodynamic conductivity tensor for 2DESs with dc drift with account for the high-frequency Hall effect (interaction of dc current with ac magnetic field). We demonstrate the limitations of the quasistatic approach which neglects this effect. With the help of electrodynamic conductivity we find a novel two-dimensional transverse electric (TE) electromagnetic mode. This mode is non-reciprocal with dispersion \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega = {\\mathbf{k}}{{{\\mathbf{u}}}_{0}}$$\\end{document} and manifests itself in lowering the reflection coefficient of 2DES at the resonance frequency. In addition, we predict birefringence of an incident evanescent TE wave on a 2DES system with drift and find hints of Cerenkov amplification in the low frequency limit. We discuss the limiting cases when the quasistatic approach is suitable.

Transverse electric waves in three-layered waveguide structure with a parabolic spatial profile of the dielectric constant, optical linear and nonlinear layers

A three-layered waveguide structure containing the Kerr nonlinear medium separated by an optical linear interlayer from a parabolic graded-index layer is considered. Exact solutions of the wave equation corresponding to several types of transverse electric waves existing in different ranges of values of the effective refractive index are found. The types of waves differ from each other by the presence or absence of oscillations in the interlayer and in the graded-index layer, as well as the form of attenuation in a nonlinear medium. The wave types obtained can be divided into two main groups. The first group includes such waves that can propagate with an arbitrarily varying effective refractive index in the allowable range of values. The second one includes such waves that can propagate at certain discrete values of the effective refractive index. Such values of the effective refractive index of waveguide modes are determined by the wavelength of the incident ray, difference between the dielectric constants of a parabolic graded-index layer, and its width. Even and odd waveguide modes are described separately. Field oscillations can be observed only in the interlayer for waves of the first group. Field oscillations can also be observed in the graded-index layer for waves of the second group. The field profile is a self-focusing nonlinear medium flatter than in a defocusing one for all types of waves. An increase in the same parameters has a different effect on the profiles of the different types of waves. The possibility of controlling the distribution of the wave energy between the layers of the waveguide structure by changing the angle of incidence is shown.

Near-unity nonreciprocal thermal radiation in biaxial van der Waals material-Weyl semimetal heterostructures

Polaritons in natural van der Waals (vdW) materials have drawn significant attention as the unique optical properties and have opened doors for various potential applications. α-phase molybdenum trioxide (α-MoO3) has been revealed as a semiconducting anisotropic vdW material that holds great promise for manipulating orthogonal in-plane phonon polariton (PhP) modes in infrared (IR). Here, we consider an attenuated total reflection (ATR) geometry consisting of an α-MoO3 layer and a Weyl semimetal (WSM) interlayer sitting on a silver (Ag) substrate. The incorperated coupling prism is selected as KRS5 (thallium bromide-iodide) that can provide a larger wavevector. The spectral responses of the proposal have been investigated using electromagnetic (EM) simulations that utilize the anisotropic rigorous coupled-wave analysis (aRCWA). Our results demonstrate that the α-MoO3 thin layer can boost the constrast between the emissivity and absorptivity in a broad range of wavelength as compared to an uncoated device. The nonreciprocity at resonance wavelength can reach near-unity for both transverse electric (TE) and transverse magnetic (TM) wave incidence. The proposed α-MoO3/WSM heterostructure suggests great potentials for thermal radiation management with different demands.

Nonreciprocal thermal emitter for transverse electric wave via attenuated total reflection

Nonreciprocal radiation is very important in essentially improving energy conversion. There have been many approaches to enhance the nonreciprocal thermal radiation properties for transverse magnetic (TM) wave incidence. However, the nonreciprocal thermal emitters for both polarization states are desired in practice, such as solar cells. In this paper, we design and demonstrate a nonreciprocal thermal emitter for transverse electric (TE) wave. By using attenuated total reflection, the nonreciprocal radiation for TE wave in Weyl semimetal film can be notably enhanced. It shows that the reciprocity between absorption and emission can be strongly broken with the difference of 0.93 at wavelength of 12 μm. Furthermore, the co-polarization and cross-polarization in the reflected wave are calculated to analyze the physical mechanism of strong nonreciprocal radiation. In addition, we discuss the influence of structural parameters, such as the thickness of the air gap, the thickness of Weyl semimetal film, the azimuthal angle and the incident angle, on the nonreciprocity. This work not only provides theoretical guidance for the design of nonreciprocal thermal emitters for TE wave, but also has promising applications in solar cells.

Analysis of the Effects of Temperature and Vertical Electric Field on the Propagation of Transverse Electric Waves in Silicene Monolayer

Analysis of the Effects of Temperature and Vertical Electric Field on the Propagation of Transverse Electric Waves in Silicene Monolayer

Switchable bi-functional metasurface for absorption and broadband polarization conversion in terahertz band using vanadium dioxide and photosensitive silicon

We proposed a bi-functional switchable metasurface based on vanadium dioxide (VO2) and photosensitive silicon. The metasurface functions as a transmissive polarization converter in its insulating state with asymmetric transmission characteristics. It attains a remarkable polarization conversion rate (PCR) surpassing 90% and a notable maximum asymmetric transmission (AT) parameter value of 0.73. This performance is observed within the frequency range from 4.31 to 7.86 THz. Dynamic regulation of PCR and AT can be achieved by adjusting the conductivity of photosensitive silicon. To illustrate the underlying factor behind the broadband polarization conversion, the surface current distribution is analyzed at 5.96 THz and 6.08 THz. On the other hand, when VO2 is in the metallic state, the metasurface transforms into a bidirectional absorber with near-perfect absorption in both illumination directions. Under forward incidence of terahertz waves, the absorption rates for the transverse electric and transverse magnetic waves are 99.3% at 3.54 THz and 93% at 3.56 THz, respectively. The physical mechanism of near-perfect absorption is explained using impedance matching theory and the electric field distribution. This research expands the applications of transmissive polarization converters within multifunctional metasurfaces, providing new avenues for their practical implementation.