To Transverse Electric Research Articles

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.

A dual functional tunable terahertz metamaterial absorber based on vanadium dioxide.

A dual-functional switchable metamaterial absorber (MMA) based on vanadium dioxide (VO2), which achieves flexible switching between broadband absorption and four-band absorption by adjusting the VO2 conductivity, was proposed. The device has a broadband absorption function when VO2 is in the metal phase, and the conductivity is 3 × 105 S m-1. Numerical simulation shows that the absorption rate of the device reaches over 90% in the frequency range of 3.36-6.98 THz. The absorber exhibits polarization insensitivity and wide-angle absorption to transverse electric (TE) and transverse magnetic (TM) waves. When VO2 is in the insulator phase, and the conductivity is 3 × 102 S m-1, the device switches to a narrowband absorber with a band-efficient absorption function. Numerical simulation shows that the device has an absorption rate of 99.7% at 2.39 THz, 98.3% at 2.83 THz, 95.6% at 3.84 THz, and 96.1% at 4.61 THz. It can be used as a sensor with high sensitivity. In addition, to verify the absorption mechanism of the absorber, we introduced impedance matching theory to analyze the device. Finally, the influence of structural parameters on the performance of resonators was investigated. Through the joint action of multi-layer structures, the proposed MMA concentrates broadband and narrowband absorption functions on one device, achieving flexible switching between tasks without changing the structure. The switchable metamaterial absorber designed through simple tuning methods has broad application prospects in stealth technology and thermal emitters. It provides a wide range of ideas for the design of terahertz functional devices.

Compact and Highly Efficient Midinfrared Fundamental-Mode Converter

A novel midinfrared (mid-IR)-integrated polarization converter with different slot alignments for transverse magnetic (TM) to transverse electric (TE) and TE to TM is reported with conversion efficiency of 100% and 50%, respectively.

Broadband THz Absorber for Large Inclination Angle TE and TM Waves

Terahertz (THz) electromagnetic wave absorbers are finding new applications both in military and civilian sectors. This is the reason why constant efforts have been made worldwide to enhance the working performance of these absorbers. One downside of the available absorbers is their response to Transverse Electric (TE) and Transverse Magnetic (TM) waves at different frequency bands. Specific strategic applications require response of an absorber in same frequency band for TE and TM electromagnetic waves, for large inclination and polarization angle of the incoming signal. In this work, we present a metasurface based THz absorber with improved functionality. The fractional bandwidth is 91.64% w.r.t the center frequency of 1.97 THz, that shows an absorptivity of more than 90%. Due to the fourfold symmetry, the absorber is polarization insensitive. It shows more than 80% absorptivity for incoming wave inclinations upto <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$60^{\circ }$</tex-math></inline-formula> . The thickness of the absorber is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> /11. The good point is that the absorber shows all these improved performance for both TE and TM incoming signals in the same frequency range. Overall, the designed absorber is a much improved version of its peers available in the literature.

High Figure of Merit in Lossy Mode Resonance Sensors with PtSe2 Thin Film

Lossy mode resonance (LMR) sensors not only support transverse magnetic mode (TM) but also respond to transverse electric (TE) polarization, which has the advantage over traditional surface plasmon resonance sensing supporting only a single TM polarization. We theoretically propose an LMR sensor that can detect the refractive index (RI) changes based on the Kretschmann configuration with PtSe2 material. The refractive index parameter of PtSe2 film is fitted through experimental measurements, and the performance of LMR sensor with PtSe2 is theoretically calculated. The figure of merit (FOM) of the sensor performance has been significantly improved, and the maximum FOM with 626 RIU−1 has been acquired.

A Hybrid Element Triband Frequency Selective Surface With High Angular Stability and Polarization Insensitivity

In this article, a triband frequency selective surface (TBFSS) with narrow band separation is proposed. Pass band frequencies of this TBFSS are 6.9, 8.63 and 10.3 GHz with fractional band width (FBW) of $\text{15.8}\%$ , $\text{13.5}\%$ , and $\text{10.9}\%$ , respectively. Low insertion losses of 0.5, 0.2, and 0.4 dB are observed in the pass bands. These resonant frequencies are adjusted in C and X bands. The unit cell (UC) dimension is $0.2\lambda _0\times 0.2\lambda _0$ which is calculated at lowest transmission zero. Hybrid structural elements are etched on two sides of Rogers 4003 C substrate with $\varepsilon _r$ of 3.38 and thickness of substrate is selected to be 0.406 mm. This design is highly obliquely stable upto $\text{75}^\circ$ . It also shows polarization insensitivity to transverse electric (TE) and transverse magnetic (TM) modes of the plane wave. An equivalent circuit is presented for better understanding of the structure and tuning purpose. A prototype is fabricated to measure the frequency response of the TBFSS. Measured and simulated scattering parameter S $_{21}$ exhibit very good match.

Extension of an FFT-Based Beam Propagation Method to Plasmonic and Dielectric Waveguide Discontinuities and Junctions

We adapted a fast Fourier transform-based Beam Propagation Method (FFT-BPM) to investigate waveguide discontinuities in plasmonic waveguides. The adaptation of the FFT-BPM to treat transverse magnetic (TM) fields requires the circumvention of two major difficulties: the mixed derivatives of the magnetic field and waveguide refractive index profile in the TM wave equation and the step-like index change at the transverse metal-dielectric boundary of the plasmonic guide and the transverse boundaries of the dielectric waveguide as well. An equivalent-index method is adopted to transform TM fields to transverse electric (TE) ones, thus enabling the benefit of the full power and simplicity of the FFT-BPM. Moreover, an appropriate smoothing function is used to approximate the step-like refractive index profile in the transverse direction. At the junction plane, we used an accurate combined spatial-spectral reflection operator to calculate the reflected field. To validate our proposed scheme, we investigated the modal propagation in a silicon waveguide terminated by air (like a laser facet in two cases: with and without a coating layer). Then we considered a subwavelength plasmonic waveguide (metal-insulator-metal MIM) butt-coupled with a dielectric waveguide, where the power transmission efficiency has been calculated and compared with other numerical methods. The comparison reveals good agreement.

Grating-Coupled Silicon-on-Sapphire Polarization Rotator Operating at Mid-Infrared Wavelengths

We provide an experimental demonstration of mid-infrared polarization rotators built on a silicon-on-sapphire platform at the mid-infrared wavelength of $4.55~\mu \text{m}$ to enable integration of quantum cascade lasers (QCLs) and detectors with slotted photonic crystal waveguide (PCW) gas sensors for on-chip optical spectroscopy applications. The polarization rotators are essential to convert the preferentially transverse magnetic (TM) polarized light from a QCL to transverse electric (TE) polarization to interface with the preferential TE-guiding slotted PCW sensors. The polarization rotator consists of an adiabatic-tapered mode converter followed by a phase shifter and a multimode interferometer that effectively transfers energy from an input fundamental TM00 polarization to a first-order TE10 polarization that is then converted to the fundamental TE00 mode. Polarization-selective sub-wavelength grating couplers are designed and fabricated to effectively couple TE or TM polarizations at the designed wavelengths into and out of the polarization rotator device for efficient device characterization. TM00–TE10 conversion efficiency of 100% is simulated. Fabrication tolerances in the phase shifter result in an experimental 80:20 splitting ratio of the measured output TE00-polarized light between two output arms.

Magnetic spin\u2013orbit interaction of light

We study the directional excitation of optical surface waves controlled by the magnetic field of light. We theoretically predict that a spinning magnetic dipole develops a tunable unidirectional coupling of light to transverse electric (TE) polarized Bloch surface waves (BSWs). Experimentally, we show that the helicity of light projected onto a subwavelength groove milled into the top layer of a 1D photonic crystal (PC) controls the power distribution between two TE-polarized BSWs excited on both sides of the groove. Such a phenomenon is shown to be solely mediated by the helicity of the magnetic optical field, thus revealing a magnetic spin-orbit interaction of light. Remarkably, this magnetic optical effect is clearly observed via a near-field coupler governed by an electric dipole moment: it is of the same order of magnitude as the electric optical effects involved in the coupling. This opens up new degrees of freedom for the manipulation of light and offers desirable and novel opportunities for the development of integrated optical functionalities.

Two Dimensional Finite Element Based Magnetotelluric Inversion using Singular Value Decomposition Method on Transverse Electric Mode

In this work, an inversion scheme was performed using a vector finite element (VFE) based 2-D magnetotelluric (MT) forward modelling. We use an inversion scheme with Singular value decomposition (SVD) method toimprove the accuracy of MT inversion.The inversion scheme was applied to transverse electric (TE) mode of MT. SVD method was used in this inversion to decompose the Jacobian matrices. Singular values which obtained from the decomposition process were analyzed. This enabled us to determine the importance of data and therefore to define a threshold for truncation process. The truncation of singular value in inversion processcould improve the resulted model.

Ultra-compact electro-absorption VO2–Si modulator with TM to TE conversion

An ultra-compact (6 μm length) electro-absorber modulator with transverse magnetic (TM) to transverse-electric (TE) conversion is proposed. The device performance is controlled by means of the semiconductor-to-metal transition of the vanadium dioxide. For the insulating state, the device performs as a TM–TE converter with insertion losses of 0.3 dB and extinction ratio of 36 dB at a wavelength of 1.55 μm. Changing to the metallic state, the TE generated component is attenuated due to the increase of losses in the VO2 and the mode mismatch. This electro-absorber modulator shows a broadband operation with an extinction ratio higher than 10 dB and insertion losses below 0.5 dB for a range of 60 nm covering the whole C-band.

Holographic waveguide display with a combined-grating in-coupler.

Volume holographic gratings are widely used as couplers in eyewear waveguide display systems, but they show a relative lower TM polarized energy compared to transverse-electric (TE) incidence. In this paper, we propose a novel holographic waveguide display system with a combined-grating as the in-coupler. When used as an in-coupler for a holographic waveguide display system, a subwavelength metal grating is designed onto the volume holographic grating to increase the total diffraction efficiency of the coupling gratings. Theoretical calculations show that this design increases the diffraction efficiency by 16.4% for TM polarization, 4.3% for TE mode, and 10.0% for unpolarized light, compared to a single volume holographic grating. Calculations also show that the use of this design as an in-coupler for a holographic waveguide system increases the luminance efficiency for these three modes by 26.8%, 9.0%, and 15.6%, respectively.

High index of refraction nanosphere coatings for light trapping in crystalline silicon thin film solar cells

Dielectric nanospheres have emerged as a promising candidate for enhancing absorption in thin film photovoltaics. In this paper, we utilize numerical electrodynamic simulations to investigate the absorption enhancements achievable in crystalline Si (c-Si) thin films of thicknesses from 100 to 2000nm from 2-dimensional close-packed silica (SiO2), silicon nitride (Si3N4), and titania (TiO2) nanosphere array coatings. We demonstrate that dielectric nanospheres can enhance the absorption in c-Si thin films by coupling incident light to transverse electric (TE) waveguide modes in the c-Si thin film. While SiO2 nanosphere arrays may achieve enhancements of less than 10% compared to ideal double pass c-Si thin films, higher index of refraction nanospheres confine light more strongly such that more nanosphere resonances may couple to waveguide modes in the c-Si. Si3N4 nanospheres may enhance ultimate efficiencies by over 40% for thicknesses ≤800nm and TiO2 nanospheres by over 50% for thicknesses ≤700nm compared to thin film structures with perfect anti-reflection coatings. This light trapping approach increases the absorption in the photoactive region without introducing additional surfaces or interfaces that increase surface recombination.

Experimental observation of a giant Goos-Hänchen shift in graphene using a beam splitter scanning method.

A giant Goos-Hänchen (G-H) shift in graphene has been theoretically predicted by previous research. In this Letter, we present experimental measurements of the G-H shift in graphene, in a total internal reflection condition, using a new method we have named "the beam splitter scanning method." Our results show that a focused light source undergoes significant lateral shift when the polarization of incident light changes from transverse magnetic (TM) to transverse electric (TE) mode, indicating a large G-H shift in graphene that is polarization-dependent. We also observed that the difference in the G-H shift for TM versus TE modes (S(TM)-S(TE)) increases with increasing thickness of graphene material. A maximum difference (S(TM)-S(TE)) of 31.16 μm was observed, which is a significant result. Based on this research, the ability to engineer giant G-H shifts in graphene material has now been experimentally confirmed for the first time to the best of our knowledge. We expect that this result will lead to significant new and interesting applications of graphene in various types of optical sensors, and more.

Three-Dimensional Anisotropic Zero-Index Lenses

We propose, design, and experimentally demonstrate three-dimensional 3-D anisotropic zero-index lenses, which can improve the directivity of traditional antennas. We show that a 3-D anisotropic zero-index lens with εu → 0 is efficient to transverse magnetic (TM) modes and can decrease the beam width of the main lobe in the E-plane; while a 3-D anisotropic zero-index lens with μu → 0 is efficient to transverse electric (TE) modes and can reduce the beam width of the main lobe in the H-plane, in which u represents the propagating direction. If such two lenses are packed together, the directivity of both E- and H-planes is significantly improved. To verify this unique property, we design and fabricate four 3-D anisotropic zero-index lenses using metamaterials in the microwave frequency and perform the experiments in the anechoic chamber. Experimental results demonstrate that the beam widths of both E- and H-plane gain patterns are greatly reduced, which have good agreements to the full-wave simulations.

Characteristics of carrier injection on polarization-dependent photoexcitation in copper phthalocyanine thin films

The carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam. The modulation efficiency of terahertz transmission due to transverse-magnetic (TM)-polarized excitation is distinctly higher than that due to transverse-electric (TE)-polarized excitation. Underlying this difference is the enhancement of carrier injection when the TM-polarized light is more transmitted through the surface of organic thin films than the TE-polarization light.

A Wide Band and High Confinement Surface Plasmon Polariton Mode Converter Based on Magneto-Optic Effects

In this paper, we have analyzed the magneto-optic (MO) effects in three layer surface plasmon polariton (SPP) slab waveguides in a longitudinal configuration which the applied magnetic field is parallel to the interfaces and the longitudinal wave propagation direction. Different configurations of layers for metal-insulator-metal (MIM) with ferromagnetic dielectric or metal layers are analyzed. We have derived the exact dispersion relation with considering MO effects for all three layers by separation of variables method. Because of coupling between SPP modes, all components of the electromagnetic field are created, hence we do not have pure TM modes in this configuration. We have shown the conversion of the transverse magnetic (TM) to transverse electric (TE) SPP mode in these anisotropic waveguides in a wide band wavelength range with high field confinement. These configurations could be used to design devices, such as isolators, modulators and switches in photonic integrated circuits (PICs).

An Ultracompact Surface Plasmon Polariton-Effect-Based Polarization Rotator

A 3-μm-long ultrasmall surface plasmon polariton-effect-based transverse-magnetic (TM) mode to transverse-electric (TE) mode polarization rotator was demonstrated both theoretically and experimentally. Effective polarization rotation with 11-dB polarization extinction ratio (PER) was achieved in fabricated devices. The insertion loss at the transition region was about 11 dB.

Finite element modeling of SHTE and PSVTM electroseismics

This work presents a numerical methodology to simulate the physical phenomena in which there is conversion between electromagnetic and mechanical (kinetic) energy. The electroseismic equations linking the diffusive electromagnetic and seismic wavefields are solved using the finite element method. The subsurface is modeled as a 2D fluid-saturated layered porous medium. It is illuminated by two different kinds of electromagnetic sources, one giving rise to transverse electric (TE) fields and the other one to transverse-magnetic (TM) fields; the former are coupled with SH and the latter with PSV mechanical displacements respectively. Examples illustrating the capabilities of the presented methodology, including partially saturated gas regions are presented.