Transverse Magnetic Polarization Research Articles

Ultra‐Low Loss Lithium Niobate Polarizer with Enhanced Anti Bound State in the Continuum

AbstractThin film lithium niobate (TFLN) has emerged as a promising platform for photonic integrated circuits (PICs). However, the polarization crosstalk is usually inevitable owing to its birefringence. Polarizers, as key polarization handling devices, are essential to ensure polarization purity in PICs. In this work, a novel ultra‐low loss polarizer is proposed and demonstrated based on the enhanced anti‐bound state in the continuum (anti‐BIC) on TFLN. With meticulously designed waveguide width, constructive interference occurs for the leaky modes, such that transverse magnetic (TM) bound mode can drastically couple into the continuum modes, leading to high propagation loss for TM polarization. Meanwhile transverse electric (TE) polarization remains bound with high optical confinement, hence low propagation loss. Furthermore, it have demonstrated that angled sidewalls can facilitate the mode conversion from bound mode into continuum mode in lithium niobate (LN), which can be an efficient method for controlling the bound mode coupling into the continuum. Ultra‐low loss of <≈0.04 dB and compact footprint of 46 µm are experimentally demonstrated from 1460 to 1600 nm for the fabricated polarizer.

Wide‐angle band‐pass FSS with high‐frequency selectivity based on SIW cavity technology

AbstractThis work proposes and investigates a wide‐angle band‐pass frequency selective surface (FSS) with two sharp sidebands. The presented FSS element is made up of three metallic layers and two substrate layers in between, which are surrounded by a substrate‐integrated waveguide (SIW) cavity. The top metallic layer is identical to the bottom layer, composed of a square patch etched with a hexagonal groove, while the middle layer is a similar patch but with rectangular notch edges. This structure achieves a second‐order band‐pass response with highly frequency selectivity on either side of the passband. At the same time, this FSS demonstrates excellent stability for both transverse electric and transverse magnetic polarizations with incident angles between 0° and 60°. The electric current and field distributions are demonstrated for deep analysis. Furthermore, an equivalent circuit model is developed to further understand the operating mechanisms. To verify the validity of the design, we construct a prototype of the SIW‐based FSS (SIW‐FSS) and measured it. There is a fair degree of agreement between the measured and simulated results. Finally, we loaded it onto the horn antenna and tested its application in filtering antennas.

Mid-infrared barium titanate electro-optic modulators based on a germanium-on-silicon platform

Mid-infrared electro-optic (EO) modulation efficiency and high-frequency performance of barium titanate (BTO) modulators on a germanium-on-silicon platform are investigated. Leveraging its exceptional Pockels coefficients, BTO exhibits remarkable EO modulation capabilities in both transverse-electric (TE) mode for a-axis growth and transverse-magnetic (TM) mode for c-axis growth. At the wavelength of 3.8 µm, the V π ⋅L for a-axis oriented BTO (TE polarization) is 1.90 V·cm, and for c-axis oriented BTO (TM polarization), it is 2.32 V·cm, which have better performance than those of the Pockels effect based EO modulators from literature. In addition, the high-frequency EO response of the modulator is simulated, and a 3-dB EO bandwidth of 62.82 GHz with the optimized traveling wave electrodes is achieved, showing promise in the high-speed MIR applications such as free-space optical communications.

Metamaterial ultra-broadband absorber in near-infrared region with decreasing thermal emission

This study is aimed to present an ultra-broadband metamaterial absorber for infrared detection and thermal emitter applications. Despite numerous studies on metamaterial absorbers, achieving ultra-broadband absorption remains a challenge. We introduce a dual-gold square array with transverse magnetic polarization and combine it with an anti-reflective (GaAs) layer and metal-insulator (gold-Al2O3) configurations. The absorber achieves over 90 % absorption between 0.63 μm and 2.90 μm, with average and effective absorptions at 94.60 % and 94.68 %, respectively. Through impedance matching theory, we validate the performance of the absorber, analyze electric field distributions to explain its mechanism, and assess manufacturing tolerance for practical application viability. Our findings reveal robust performance of the metamaterial absorber across a wide spectral range, including insensitivity to incidence angles, with absorption over 80 % in 20–60°, highlighting its potential in the infrared detection and the thermal emitter.

Polarization dependent exciton-plasmon coupling in PEA2PbI4/Al and its application to perovskite solar cell.

This paper reports the strong coupling between Al nanostructure and two-dimensional (2D) layered perovskite PEA2PbI4 (PEPI) films. The high exciton binding energy of 118 meV and long carrier lifetime of 216 ps are characterized from the 2D PEA2PbI4 film, which indicates that the excitons in perovskite are robust and can couple to metal plasmons. The ordinary and extraordinary optical dispersions are revealed from the anisotropic 2D perovskite. The transmission spectra of PEA2PbI4/Al nanoparticle arrays are simulated under different polarization excitations, and the typical anti-crossing behaviors originating from exciton-plasmon strong coupling are demonstrated. We found that compared with transverse magnetic (TM) polarization, transverse electric (TE) polarization excitation is more conducive to the realization of exciton-plasmon coupling with a larger Rabi splitting. Furthermore, the PEA2PbI4/Al nanoparticle arrays are proposed, which present polarization-dependent local electrical field enhancement due to the exciton-local surface plasmon polariton coupling. Additionally, it is noticed that the proposed plasmonic structure increases the photo-generation rate inside the active material with improved current density. Therefore, the 2D proposed plasmonic design increases the power conversion efficiency (PCE) with an enhancement of 3.3% and 1.3% relative to the planar structures for TE and TM polarizations, respectively. This study provides a deeper understanding of polarized exciton-plasmon coupling properties, promoting the development of the field of plasmon and providing guidance for the design and preparation of efficient optoelectronic devices.

Using archived magnetotelluric data for geologic interpretation in the Transdanubian Region

We provide a key magnetotelluric section, composed of archived magnetotelluric data along a NW-SE profile in Transdanubia, Hungary. For the interpretation of the key section, observations from raw magnetotelluric data and inversion results were used. In addition, other geophysical-geological information was also considered to confirm the conclusions based on the electrical resistivity sections. All this information was combined to identify the main structural lines and geologic units along the profile. Main structural lines observed on the resistivity sections are the Alpokalja line, Rába line, Balaton line, Kapos line, and Mecsekalja line. Geologic units that can be delineated due to their resistivity contrast include the Lower and Upper Austroalpine Units, the Transdanubian Range Unit, the Mid-Hungarian Megaunit, the Tisza Megaunit and sedimentary rocks filling the sub-basins of the Miocene Pannonian back-arc basin. The inversion results of the transverse magnetic (TM) polarization mode and the phase-depth sections of the raw data were found to be the most suitable for detecting the morphology and identifying the depth of the Pre-Cenozoic basement along the profile.

3D-printed multi-material pyramids for broadband electromagnetic wave absorption

Designing and manufacturing broadband electromagnetic wave-absorbing materials represents one of the significant approaches to address electromagnetic pollution issues. This study utilizes three different PLA-based composite absorbing materials to prepare multilayer pyramid structures employing 3D printing technology. Results indicate that with material composition Z1-GT6-N8, material layer height (h) of 6 mm, and pyramid base length (L) of 36 mm, the fabricated structure achieves a minimum reflection loss of −24.19 dB with an effective absorption bandwidth of 14.21 GHz, demonstrating outstanding absorption performance. It is noteworthy that regardless of the incident angle increasing from 0° to 50°, the equivalent absorption bandwidth (EAB) for both transverse electric (TE) and transverse magnetic (TM) polarizations remains greater than 10 GHz, indicating excellent angle stability. The broadband and efficient electromagnetic wave (EMW) absorption characteristics exhibited by this absorber can be attributed to its outstanding impedance matching performance and the integration of multiscale loss mechanisms.

Miura-ori based reconfigurable multilayer absorber for high-efficiency wide-angle absorption.

Radar stealth structures that can achieve high-efficiency wide-angle absorption are key components of future military equipment. However, it is difficult for both planar and three-dimensional (3D) absorbers to achieve efficient absorption in a large incidence angle range. The multilayer reconfigurable absorber component based on Miura origami provides a unique solution. First, the multilayer origami absorber is parameterized in the simulation software. Each origami structure is covered with resistive films that fit the panels. Geometric constraints are satisfied among the multilayer structures. They support reconfigurability in the range of continuous states (as opposed to discrete states), which is conducive to finding the folded state with a more efficient absorption rate within the frequency band. Secondly, the designed structure does not require a specialized mechanically supported multilayer origami absorber. In addition, the equivalent analogue circuit method is used to analyze the efficient absorption of multilayer origami under oblique incidence. Finally, our proposed absorber satisfies the requirements of multiple absorption metrics: broadband, high efficiency, wide incidence angle, and polarization insensitivity. As the validation, we simulated and fabricated a double-layer origami absorber. Our proposed origami absorber can maintain an absorption rate of more than 90% for both transverse electric (TE) and transverse magnetic (TM) polarizations in the operating frequency band (5-20 GHz) over a wide range of incidence angles (0°-70°). When the incidence angle qinc = 40°, the double-layer origami absorber (q1 = 90°, α1 = 60°, and a2 = 75°) can achieve at least 10 dB reflection reduction of -18 dB and -20 dB in TE and TM modes, respectively. The proposed origami absorber provides a reference for the design of other absorbers.

Polarization-independent nonreciprocal thermal radiation by cylindrical grating structure

Due to the significant application value of nonreciprocal thermal radiation in energy collection and conversion, it has always been an active research topic. The current research on polarization-independent nonreciprocal thermal radiation is characterized by low efficiency and a notable disparity in nonreciprocal efficiency between transverse electric (TE) and transverse magnetic (TM) polarizations. To address this issue, a polarization-independent nonreciprocal thermal radiation based on the two-dimensional grating structure is proposed, which is composed of silicon cylindrical grating ridges, magneto-optical materials InAs, and metal Ag. By the rigorous coupled-wave analysis (RCWA), the nonreciprocal efficiency exceeds 90 % at a wavelength of 11.763 μm under both TE and TM polarizations. Meanwhile, the difference in nonreciprocal efficiency between the two polarizations is less than 1 %. Through an examination of the magnetic field and electromagnetic distribution at resonance peaks that are polarization-independent, as well as an analysis of coupling mode theory, we have uncovered the underlying physical mechanisms responsible for this phenomenon. The device is capable of sustaining optimal performance across a wide range of structural parameters, offering a significant role for manufacturing applications. The research proposed in this article provides a novel approach for designing efficient polarization-independent nonreciprocal thermal radiation.

Broadband metasurface bandpass filter with wide angular stability for the Ku-band

Broadband spatial spectral filters have consistently been in high demand due to their diverse and extensive applications across numerous fields in the past decades. In this paper, a broadband metasurface (MS) bandpass filter (BPF) with wide angular stability was proposed and investigated at Ku band. The unit-cell of the proposed MS BPF is consisted of the cross-shape structure (CSS) sandwiched with two layer identical four-square-patches (FSPs) and dielectric substrates. Finite element method (FEM) simulation indicates that the designed MS BPF has distinctive broadband transmission coefficient of over −3 dB from 12.75 GHz to 16.8 GHz with a relative bandwidth of 27.4 %, which is basically consistent with equivalent circuit model (ECM) calculation. The physical mechanism underlying the proposed MS BPF is elucidated through the introduction of impedance matching theory, electric field and surface current analysis. Further numerical simulation has confirmed that the designed broadband MS BPF exhibits valid performance across a wide spectrum of incident angles, encompassing both transverse electric (TE) and transverse magnetic (TM) polarizations. Finally, a prototype has been fabricated for measurements, and the proposed design has been validated through comprehensive analysis of simulated and measured results. Due to its excellent transmission properties, the proposed MS BPF shows potential application in such as radar, remote sensing, and satellite communication.

Integrated optical waveguides for quantum photon gates at a wavelength of 810 nm

Subject of study. The optical losses in waveguides designed for creating quantum photon gates at a wavelength of 810 nm were investigated. Aim of study. The aim of the study was to create integrated optical single-mode waveguides for quantum photon gates at a wavelength of 810 nm and to estimate optical losses acceptable for maintaining the necessary degree of photon-pair entanglement. Method. The waveguides were manufactured through thermal diffusion of titanium ions into a substrate composed of an X-slice of nominally pure lithium niobate (LiNbO3). Optical losses were estimated by experimentally measuring the loss per unit length of the waveguide. Optical radiation was coupled into and out of the waveguide using fiber segments, with one end connected and the other cleaved. A drop of immersion liquid was applied between the cleaved fiber and waveguide end, and measurements were performed for both polarization modes. Main results. Six groups of samples were produced, each containing waveguides with strip widths of d=3.0, 2.0, and 1.5 µm. The measured optical losses in the manufactured waveguides indicated that those with a titanium strip width of d≈3 µm exhibited the lowest losses. The estimated minimum optical losses for transverse magnetic and transverse electric polarization were approximately 0.20–0.25 and 0.1 dB/cm, respectively. Practical significance. The waveguides manufactured with a strip width of approximately 3 µm can be used to create quantum photonic gates in an integrated optical design. The chosen wavelength of 810 nm offers potential for near-future development of photonic gates, as one of the most accessible methods for generating entangled photon pairs involves using a 405-nm laser followed by wavelength doubling through a nonlinear beta-barium borate crystal.

Graphene-based tunable tri-band terahertz refractive index sensor

A tunable tri-band terahertz refractive index sensor based on graphene is proposed and designed. The structure of the sensor comprises a gold (Au) substrate layer, a dielectric layer (Topas), and a graphene pattern layer. The numerical simulation results demonstrate that the sensor exhibits three narrowband absorption peaks at 1.68, 3.82, and 4.78 THz, and the corresponding absorption rate can reach 99.9%, 98.0%, and 97.9%, respectively. By adjusting the Fermi level of graphene, the resonant frequency of the sensor can be effectively tuned. Notably, due to the rotational symmetry of the structure, the sensor shows insensitivity to transverse magnetic and transverse electric polarizations of incident light. By varying the refractive index of surrounding analytes, the sensor’s sensitivity and Figure of Merit (FOM) are studied. The sensitivities of the three resonance peaks are 0.59, 1.19, and 1.38 THz/RIU, with corresponding FOM values of 2.57, 3.40, and 6.58, respectively. Furthermore, the feasibility and effectiveness of the designed sensor in practical applications are verified by testing five types of samples. These findings indicate that the proposed sensor has superior performance in sensitivity and selectivity, which makes it have a great potential for applications in the fields of material characterization, environmental monitoring, and biomedicine detection in the terahertz band.

Double-sided structure grating for dual-functional polarizing or non-polarizing splitter

In this paper, a novel bidirectional dual-functional metal-dielectric reflective grating with a double-sided structure is described, which can achieve transverse-electric (TE) polarization in the -1st order and transverse-magnetic (TM) polarization in the 0th order as a polarizing beam splitter in the upper part of the grating or TE and TM polarizations in the -1st order with polarization-independent property in the lower part of the grating. The proposed grating works at wavelength 1550 nm under Littrow mounting. Rigorous coupled-wave analysis (RCWA) is used to optimize grating parameters. The upper part can achieve diffraction efficiencies of 99.53% and 99.11% for TE polarization in the -1st order and TM polarization in the 0th order, respectively. In addition, the extinction ratios of -1st order and 0th order are 58.87 dB and 52.02 dB, respectively. The lower part can achieve diffraction efficiencies of 99.41% and 99.26% for TE and TM polarizations in the -1st order, respectively. Furthermore, wide incident wavelength and angular bandwidths can be obtained in both the upper and lower parts. Such a high-efficiency dual-functional grating has a wide range of applications in optical systems.

Low-Loss Buried InGaAs/InP Integrated Waveguides in the Long-Wave Infrared.

In this work, we present a photonic integrated platform based on buried InGaAs waveguides with InP cladding that operates over a large mid-infrared (mid-IR) spectral range. Thanks to wet-etch fabrication patterning and Fe doping, low propagation losses below 1.2 dB/cm (0.3 cm-1 loss coefficient) have been obtained between 4.6 and 11.2 μm wavelengths (890-1960 cm-1 wavenumber), in both transverse electric (TE) and transverse magnetic (TM) polarization modes. The possibility of monolithically integrating such waveguides with mid-IR sources offers promising perspectives for developing broadband, homogeneously integrated systems.

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.

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.

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%.

Rotationally symmetric transverse magnetic vector wave propagation for nonlinear optics

In this paper the theory and simulation results are presented for 3D cylindrical rotationally symmetric spatial soliton propagation in a nonlinear medium using a modified finite-difference time-domain general vector auxiliary differential equation method for transverse magnetic polarization. The theory of 3D rotationally symmetric spatial solitons is discussed, and compared with two (1 + 1)D, termed “2D” for this paper, hyperbolic secant spatial solitons, with a phase difference of π (antiphase). The simulated behavior of the 3D rotationally symmetric soliton was compared with the interaction of the two antiphase 2D solitons for different source hyperbolic secant separation distances. Lastly, we offer some possible explanations for the simulated soliton behavior.

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.