Transverse Electric Polarization Research Articles

Design of TE-polarized resonant Bessel-beam launchers for wireless power transfer links in the radiative near-field region

Abstract Resonant Bessel-beam launchers (BBLs)are radiating devices constituted by a cylindrical metallic cavity with a partially reflecting sheet (PRS) on top. Millimeter-wave resonant BBLs typically exhibit transverse magnetic (TM) polarization due to the use of coaxial probes as feeders and homogenized metasurfaces as PRS. Launchers showing either a purely transverse electric (TE) or a hybrid (quasi-TE) polarization have recently been proposed for realizing wireless power transfer (WPT) links in the radiative near-field region at millimeter waves. The former are obtained by means of a radial slot array as a feeder and a homogenized metasurface as a PRS. The latter are obtained by using a loop antenna as a feeder and an annular strip grating in the homogenization limit as radiating aperture. In this work, based on an original semi-analytical model, such a metasurface is demonstrated to show a dichroic behavior. This interpretation explains the improvement in terms of polarization purity with respect to more nondichroic conventional homogenized metasurfaces. The behavior of the annular strip grating under a pure TM polarization is tested with a coaxial feeder, whereas its behavior under a pure TE polarization is tested by means of the radial slot array feeder. Results confirm the validity of the proposed analysis, which is finally exploited to evaluate the WPT performance.

Polarization-independent Spatial Kramers-Kronig medium for omnidirectional reflectionless absorption of unpolarized light

Spatial Kramers-Kronig (KK) media offer a possible route to obtain omnidirectional light absorption within a thin layer of material. However, the experimental realizations are typically limited to a specific polarization, i.e., either transverse electric (TE) or transverse magnetic (TM), hence lacking specific implementations for the absorption of unpolarized light. In this work, we propose theoretically and demonstrate experimentally a polarization-independent KK medium which performs omnidirectional reflectionless absorption for both TE and TM polarized waves. Our design makes use of a special matryoshka metamaterial, whose electric and magnetic responses can be independently controlled with minimized crosstalk. To extend the absorption spectrum, the inner truncation boundary of the KK medium is set at a position far away from the spatial Lorentz resonance, where the constitutive parameter of the metamaterial remains unitary over a broad frequency band. A mini anechoic chamber, 6.83-wavelength in diameter, is constructed using the designed annulus-shaped KK medium. The measured fields for both TE and TM polarizations confirm the polarization-independent omnidirectional and nearly reflectionless absorption in a broadband frequency range.

Design and analysis of polarization-insensitive molybdenum-based ultra-wideband solar energy absorber with wide-incident-angle

We introduce an ultra-wideband absorber with a molybdenum and Al2O3 multilayer structure for solar energy harvesting. The proposed structure could maintain its structural integrity at high temperatures thanks to the refractory materials used in its construction. Under normal incidence of optical waves, absorption of more than 90% is achieved throughout a broad range of wavelengths from 300 nm to approximately 3177 nm with a bandwidth of 2877 nm which covers ultraviolet, visible, and near-infrared spectral bands. The average absorption in that band is calculated to be 96.46%. The proposed design’s symmetrical characteristic makes the absorber insensitive to the polarization of the incident optical wave. Furthermore, throughout a broad range of optical wave angles of incidence for both transverse electric and transverse magnetic polarizations, the absorber supports absorptivity greater than 80%.

Optical and fluorescent properties in Er, Yb:YAG double-line waveguide by femtosecond laser direct writing

This paper reports the double-line waveguides in Er,Yb:YAG prepared by femtosecond laser (fs-laser) writing at 1030 nm, 450 fs pulse and 100 kHz repetition rate. When light propagates at 632.8 nm along transverse electric (TE) and transverse magnetic (TM) polarization, efficient single-mode guidance is demonstrated in the double-line structures. The minimum transmission loss is as low as 0.98 dB/cm in waveguide with space of 18 μm. The structural modifications in damaged tracks and strain-affected regions were characterized by confocal micro-Raman spectroscopy, and the refractive index variations were analyzed. The corresponding fluorescence emissions of Er3+ and Yb3+ are investigated in the Er,Yb:YAG double-line structure.

Design of functionally gradient metastructure with ultra-broadband and strong absorption

Rational design principles for ultra-broadband lattice-based metastructure absorbers (MMAs) remain scarcely explored, including elucidation of the governing absorption phenomena. This work presents Octet truss lattices gradient-tailored to achieve highly efficient wide-spectrum electromagnetic (EM) wave mitigation. The optimized 15 mm thick three-dimensional printed architectures comprise three stacked sub-layers with graduated densities spanning a reflective backing. Analysis of unit cell EM responses as a function of geometric parameters facilitates concurrent broadband absorption and minimal mass. Consequently, ultra-wideband absorption below −10 dB persists from 2.84 to 40.0 GHz under normal incidence, with strongly enhanced attenuation below −15 dB between 8.51 and 40.0 GHz. Additionally, consistent absorption capacity endures up to 60° for both transverse electric (TE) and transverse magnetic (TM) polarizations, empowered by the intricate conductive networks established through wave interactions. The unique combination of additive manufacturing, hierarchical metamaterial engineering, and physical insights provides a versatile strategy for customized broadband absorption systems across application domains.

Lossy Mode Resonance Sensors Based on Anisotropic Few-Layer Black Phosphorus.

Lossy mode resonance (LMR) sensors offer a promising avenue to surpass the constraints of conventional surface plasmon resonance (SPR) sensors by delivering enhanced label-free detection capabilities. A notable edge of LMR over SPR is its excitation potential by both transverse electric (TE) and transverse magnetic (TM) polarized light. Yet this merit remains underexplored due to challenges to achieving high sensing performance under both TM and TE polarization within a singular LMR model. This study introduces a theoretical model for an LMR prism refractive index sensor based on a MgF2-few layer black phosphorus-MgF2 configuration, which can achieve angular sensitivity nearing 90° refractive index unit-1 (RIU-1) for both polarizations. Leveraging the distinct anisotropic nature of black phosphorus, the figure of merit (FOM) values along its two principal crystal axes (zigzag and armchair) show great difference, achieving an impressive FOM of 1.178 × 106 RIU-1 along the zigzag direction under TE polarized light and 1.231 × 104 RIU-1 along the armchair direction under TM polarized light. We also provide an analysis of the electric field distribution for each configuration at its respective resonant conditions. The proposed structure paves the way for innovative applications of anisotropic-material-based LMR sensors in various applications.

Broadband high-contrast-grating-type waveplates for the terahertz range

The high-contrast-grating waveplates utilizing high contrast between silicon and air refractive indexes were developed in order to perform as a quarter wave and a half wave plate in the selected THz frequency range. The waveplates possessed anti-reflective properties due to the specific inclination of the walls both in parallel and in perpendicular direction to grating axis, efficiently suppressing the reflection losses caused by air-dielectric interface for both transverse magnetic and transverse electric polarizations. Moreover, significant reduction of the transmittance gap was achieved between both polarizations while mitigating overall Fabry-Perot effect. Validation of the concepts was carried out by measuring transmission amplitude and phase spectra of the fabricated samples in a broadband of THz time-domain spectroscopy and vector-network-analysis systems considering also some real applications.

A wide-angle broadband dual-polarization electromagnetic absorbing structure based on the carbonyl iron powder/polydimethylsiloxane composites

Electromagnetic absorbing structure with wide-angle and broadband absorption plays a vital role in radar stealth. Hence, a novel gradient composite multilayer absorbing structure (GCMAS) is designed and fabricated by a simple and low-cost direct ink writing (DIW) 3D printing technology. The GCMAS consists of the CIP/PDMS composites composed of carbonyl iron powder (CIP) and polydimethylsiloxane (PDMS), which have outstanding flexibility, chemical and thermal stability. By metastructure design of gradient composites, a material-structure–function integrated absorbing structure with 50 wt% CIP/PDMS in the top layer, 60 wt% CIP/PDMS in the middle two layers, and 70 wt% CIP/PDMS in the bottom two layers is obtained. Simulations demonstrate that the designed GCMAS with the thickness of 13 mm can achieve the −10 dB absorbing bandwidth in the frequency range from 2.88 to 38.24 GHz, and the absorbing bandwidth corresponding to −15 dB in 2.97–36.17 GHz. The maximum reflection loss is −42.17 dB at 22.96 GHz. Experiments demonstrate that the GCMAS can achieve the −10 dB absorbing bandwidth in 3.6–40 GHz. Moreover, the GCMAS also can maintain the broadband and strong absorbing performance with incident angle from 0° to 50° for transverse electric (TE) polarization and 0° to 60° for transverse magnetic (TM) polarization. This work provides a promising strategy for the fabrication of functional gradient composites and flexible or bendable absorbing structure, which have great potential in satellite communications and radar stealth.

Ultrathin tunable UWB metasurface absorber design by exciting plasmonic modes in bilayer graphene stack

This work presents a graphene-based ultra-wideband (UWB) tunable metasurface absorber (MSA) consisting of top patterned graphene (Gpat) and bottom continuous graphene (Gcont) separated by a 2 μm thick silicon dioxide (SiO2) substrate. An absorptivity (Af) ≥ 90 % from 0.1 to 14 THz (fractional bandwidth = 197.2 %) has been achieved in three steps: (i) Fabry-Perot cavity mode has been generated near 0.1 THz using bilayer graphene stack, (ii) multiple plasmonic modes have been excited by engraving resonant slots on Gpat and (iii) plasmonic coupling strength has been enhanced between Gpat and Gcont by adjusting SiO2 substrate's thickness. The excited plasmonic modes show high absorption due to the generation of localized surface plasmon polariton (LSPP) waves. The fourfold symmetry in design nullifies the effect of the polarization angle (ϕ). Interestingly, the orthogonal modes' excitation helps to achieve similar Af response under both transverse electric and transverse magnetic polarizations for incidence angle (θ) up to 60°. Further, an effective DC biasing mechanism has been devised to tune the chemical potential (μc) of the interconnected Gcont, which ensures common DC bias between unit cells. A DC voltage from 0 to 10.2 V can vary μc (Bottom) from 0 to 1 eV to provide frequency tunability.

Thermally tunable nonreciprocal radiation in lithography-free vanadium dioxide-dielectric-Weyl semimetal stack

Nonreciprocal thermal radiation (NTR) holds great promise in revolutionizing energy harvesting and conversion process, has become a hot topic of various research fields ranging from renewable energy, molecular sensing, to thermal circuitry and camouflage. Despite intensive effort into enhance the nonreciprocal response, static manipulation of NTR has limited the potential application, dynamic control of thermal radiation is highly demanded. Here, by using a multilayered stack comprised of vanadium dioxide (VO2) thin film, germanium (Ge) spacer layer, Weyl semimetal (WSM) layer terminated by molybdenum (Mo) substrate, we propose a thermally tunable nonreciprocal emitter. The effects of the incident angle (θi), azimuthal angle (ϕi), and the thickness of each layer for the VO2/Ge/WSM stack on the characteristics of thermal radiation have been discussed thoroughly. Dominant peaks and dips of nonreciprocity have been obtained with an incident angle of θi=60° and azimuthal angle of ϕi=0°. A switching effect between the near-unity nonreciprocity (”ON”) and zero nonreciprocity (”OFF”) states are induced when the temperature increases from 20 °C to 68 °C. It is shown that the magnitude and sign of the nonreciprocity can be managed simultaneously for transverse electric (s-) and transverse magnetic (p-) polarizations. The proposed structure shows good near-unity nonreciprocity stability in a wide range of θi and ϕi. This structurally lithography-free nonreciprocal thermal emitter not only provides the ability to tune nonreciprocal radiative properties, but also leads to the possible development of power scavenging and conversion devices.

Enhanced deep ultraviolet light emission from AlGaN based nanowire with bowtie antenna array

The performance of conventional AlGaN based deep ultraviolet nanostructure has been hindered by low light emission efficiency. In this study, we demonstrate that the integration of a plasmonic aluminum (Al) bowtie antenna array with a high AlN content AlGaN based nanowire can potentially achieve a 42% and 45% enhancement in light emission at 275 nm under transverse electric (TE) and transverse magnetic (TM) polarization excitation, respectively. This enhancement is realized by carefully optimizing the nanowire diameter, as well as the size and position of the Al bowtie antenna array. The optimized dimensions of the nanowire facilitate light emission enhancement at 275 nm through dielectric resonance. Moreover, the integrated nanowire/antenna array system further increases light emission efficiency by exploiting local surface plasmon resonances. This integrated system holds promise for designing nano-photonic devices with precisely controlled responses.

Material extrusion 3D printing of large-scale SiC honeycomb metastructure for ultra-broadband and high temperature electromagnetic wave absorption

Electromagnetic (EM) wave absorbing materials have been widely used in various equipment to reduce the interference caused by EM waves. However, current EM wave absorbing materials are limited by narrow absorption bandwidth under high temperatures due to a lack of structural design. Herein, SiC ceramic and large-scale SiC honeycomb metastructure were monolithically fabricated by material extrusion 3D printing. The real permittivity and imaginary permittivity of as-obtained SiC ceramic approached 10 and 2.3 within the frequency of 2–18 GHz. After optimized structure design, the as-obtained SiC honeycomb metastructure exhibited broadband EM performance of −10 dB effective bandwidth from 4.85 to 39.49 GHz (34.64 GHz) when the incident angle was 60° at room temperature. Moreover, the as-obtained SiC honeycomb structure had a stable broadband −10 dB effective bandwidth of above 35 GHz when the incident angle is 60° even after in-situ 1000 °C and ex-situ 1600 °C erosion in the air atmosphere. Broadband EM wave absorption under oblique incident wave was also achieved from 30° to 60° both in transverse electric (TE) polarization and transverse magnetic (TM) polarization. This novel strategy unravels the potential of additive manufacturing of high-performance EM wave absorbers for high temperature environment applications.

Optimization of the reflection in the optical coupling between high numerical aperture fibers and photonic integrated circuits

The optical coupling in silicon Photonic Integrated Circuits (PICs) remains one of the main topics in the improvement of the performance of these devices. Highly demanding parameter specifications, such as loss, reflection, and bandwidth, drive the continuous search for optimization. The use of High Numerical Aperture Fibers (HNA fibers) to couple light in small diameter mode edge couplers, is one of the existing technologies that address the coupling challenge. We demonstrate, using Eigenmode Expansion (EME) and Transfer Matrix Method (TMM) simulations, that the Optical Return Loss (ORL) of this coupling approach can be made as low as −45 dB for both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations, simultaneously. The results from our TMM model agree well with a commercial solver one and are faster (six orders of magnitude) and more computationally efficient. It is shown that the refractive index in the TMM should be corrected to compensate for the Gouy phase shift in the non-guided sections of the optical coupling. Additionally, the reflection pattern, as a function of the gap between the fiber and the PIC, provides a way to control the distance of the fiber to avoid packaging-related problems.

Absorption loss properties and Stokes shifts of InGaAs-based self-assembled well-wire-hybrid quantum structures

Stokes shift is an important physical property relating to emission and absorption of light-emitting diodes, which reflects photon self-absorption situation and affects the device performance. Nowadays, it is becoming more and more difficult to change Stokes shift and relevant physical properties to further improve device performance with traditional quantum structures from increasing requirements in application. Therefore, hybrid quantum structures have attracted an attention recently. However, the properties related to Stokes shift in the new configurations have not been revealed so far. In this paper, we investigate the absorption loss and Stokes shift of the newly proposed InGaAs self-assembled well-wire-hybrid quantum structure. By designing a new absorption loss measurement approach, we can conveniently extract internal optical mode loss of a quantum structure and explore its Stokes shift with the measured absorption spectra. Our findings reveal that the presence of quantum wires in the structure can significantly reduce the Stokes shift difference between transverse electric and transverse magnetic (TM) polarizations from 66.7% for a traditional quantum well to 15.4%. It suggests the potential for the reduction of TM-mode photon self-absorption in a compressive-strain quantum structure. This phenomenon offers new prospects for the development of polarization-insensitive devices.

Compact and low-insertion-loss polarization beam-splitting multimode filter using pixelated waveguides.

A polarization beam-splitting multimode filter using pixelated waveguides has been presented and experimentally demonstrated in this paper. Finite difference time domain method and direct binary search optimization algorithm are employed to optimize pixelated waveguides to realize compact size, broad bandwidth, large extinction ratio, low insertion loss, and good polarization extinction ratio. Measurement results show that, in a wavelength range from 1520 to 1560 nm, for the fabricated device working at transverse-electric polarization, the measured insertion loss is less than 1.23 dB and extinction ratio is larger than 15.14 dB, while for transverse-magnetic polarization, the corresponding insertion loss lower than 0.74 dB and extinction ratio greater than 15.50 dB are realized. The measured polarization extinction ratio larger than 15.02 dB is achieved. The device's length is only 15.4 µm.

Microwave absorption performance for Cu, Co, and Ti co-doped SrFe12O19 as a function of incident angle

Microwave-absorbing materials (MAMs) are essential for mitigating the unwanted effects of electromagnetic interference and microwave pollution. MAMs are also used in 5G technology, energy harvesting, information security, and military technology (such as reduced radar cross-section). In this work, SrFe12–2xCux/2Cox/2TixO19 samples, prepared by using a ball mill and heat treatment method, showed their superior microwave dissipation features in both effective absorption bandwidth (EAB) and reflection loss (RL) values for the microwave incident angle of 0°, where EAB and RL values reached 15.90 GHz and −42.86 dB, respectively. The optimum RL values would change with the variation of the incident microwave angle. RL values at a specific oblique angle could exhibit better RL values for both transverse electric (TE) and transverse magnetic (TM) polarization modes, except for the x = 0.15 (SrM15) sample for TE mode. In detail, the x = 0 (SrM0) sample achieved the lowest RL value of −71.28 dB for the incident angle of 20° in the TE polarization mode, which was much better than that of the normal incident. The RL of the SrM15 sample in TM mode was significantly enhanced and reached a value of −66.48 dB for an incident angle of 10°. The increase in the RL values resulted from the superior values of complex permittivity and permeability and their matching. In addition, the improvement in RL values could be attributed to the increase in incident and refraction angles as well as the longer pathway of the microwave inside the samples. These discoveries also illustrate that SrFe12–2xCux/2Cox/2TixO19 samples hold promise for various everyday applications, even when exposed to oblique angle variation.

High-performance absorber with substitutable materials for short-wave infrared sensing

The optical absorption device plays a crucial role as a component of the infrared astronomical telescope and possesses a significant impact on astronomical observations. A simple metamaterial absorber with substitutable middle materials is made for short-wave infrared sensing. The absorber is designed as a hollow square column, using a patterning approach for the top-layer structure of metamaterials. The absorption characteristics are verified using the impedance matching method, which involves extracting S-parameters and then performing inverse calculations to determine the absorber’s equivalent impedance. The result shows the highest absorption peak is at 3.25 μm, reaching 99.71%, with an impressive average absorption rate of 99.01% between 1.52 and 3.66 μm. The results demonstrate that this absorber shows polarization insensitivity while maintaining high absorption even at large angles of incidence. The distribution of the electromagnetic field within the absorber, the electromagnetic losses within individual layers, and their impact on the absorptive performance are analyzed in detail. Polarization angles, transverse magnetic polarization, and transverse electric polarization are further explored. The parameters of each layer have been discussed. An investigation of the intermediate dielectric layer has been conducted. The proposed absorber shows the potential to achieve exceptional absorption performance under various dielectric conditions, rendering it a promising candidate for use in astronomical observation, medical tests, infrared detection, invisible short-wave infrared systems, radar and various optical devices.

Polarization-independent dislocation modes in photonic crystals

Recently, gapless dislocation modes along the synthetic translation dimensions are proposed in two-dimensional photonic crystals. However, gapless dislocation modes are specific to either transverse magnetic or transverse electric polarization, hindering their utility in polarization-independent optics. In this work, we achieve polarization-independent dislocation modes in the crossing of gapless dislocation modes of two polarizations. The frequencies of TM and TE polarized dislocation modes change with the translation parameter. By selecting suitable translation parameter, we realize TM and TE polarized dislocation modes at the same frequency within a single dislocation. We not only realize dual-polarization gapless dislocation modes but also investigate their eigen field characteristics with different frequencies. Our work offers a novel strategy for developing polarization-independent topological photonic devices.

A tunable flat terahertz lens using Dirac semimetals: a simulation study

We propose and design a flat and tunable terahertz lens achieved through a two-dimensional photonic crystal composed of an array of rods made of a Dirac semimetal placed in air as the background medium. The structure of interest is a graded index photonic crystal, made possible by the slight variations in the rods’ radii in a direction perpendicular to the direction of the light propagation. Dirac semimetals' ability to respond to variations in their Fermi energy level manifested as a change in the refractive index provides the tunability of our proposed lens. The interaction of electromagnetic waves with the designed structure is investigated for both transverse magnetic and transverse electric polarizations using two-dimensional finite-difference time-domain method.

A highly efficient and accurate numerical method for the electromagnetic scattering problem with rectangular cavities

This paper presents a robust numerical solution to the electromagnetic scattering problem involving multiple multi-layered cavities in both transverse magnetic and electric polarizations. A transparent boundary condition is introduced at the open aperture of the cavity to transform the problem from an unbounded domain into that of bounded cavities. By employing Fourier series expansion of the solution, we reduce the original boundary value problem to a two-point boundary value problem, represented as an ordinary differential equation for the Fourier coefficients. The analytical derivation of the connection formula for the solution enables us to construct a small-scale system that includes solely the Fourier coefficients on the aperture, streamlining the solving process. Furthermore, we propose accurate numerical quadrature formulas designed to efficiently handle the weakly singular integrals that arise in the transparent boundary conditions. To demonstrate the effectiveness and versatility of our proposed method, a series of numerical experiments are conducted.