TM Modes Research Articles

Dispersion analysis of grounded dielectric slab coated with double positive (DPS) / double negative (DNG) material

The present work investigates the dispersion characteristics both for TM and TE modes in a grounded dielectric slab coated with double positive (DPS) material and double negative (DNG) material. The outermost dielectric layer is assumed to be free space. By employing proper boundary conditions at interfaces, dispersion relations for the aforementioned structure for both TM and TE modes are derived. Additionally, surface waves at the interface of free space and DPS/DNG coating are investigated. Existence of mode degeneracy for DNG/DPS combination has been discussed based on dispersion analysis.

Far-fields and Scaling Laws of Two-Dimensional TM Modes in Dirac-vortex Topological Cavity

Far-fields and Scaling Laws of Two-Dimensional TM Modes in Dirac-vortex Topological Cavity

Behavior of TE and TM propagation modes in nanomaterial graphene using asymmetric slab waveguide

Abstract In this article, the conduction of transverse electric/transverse magnetic (TE/TM) propagation modes in nanomaterial graphene utilization of asymmetric dielectric slab waveguide was studied in terms of their applicability in optical fiber communication. Nano-graphene film was deposited on silica substrate and air cladding. Three layers were exposed to electromagnetic waves with a 1.55 µm wavelength and 1 µm thick nanographene film, silica, and air covering to study the performance and optical properties of graphene nanomaterials. The models were influenced by factors such as attenuation wavenumbers, cut-off frequency, mode number, propagation wavenumbers, skin depth, and angles of total internal reflection. The impact of these parameters was assessed through numerical analysis, revealing significant correlations. The modes generated ten numbers of TE and nine numbers of TM mode dependent upon the structure of nanographene, with low loss propagation wavenumber. As the TE/TM modes increase, the decay wavenumbers of the cladding and substrate parameters diminish. This indicates that the magnetic and electric fields undergo extremely rapid decay beyond the film region, which leads to the skin depth for higher TE/TM modes traveling longer distances in the cladding and substrate than do lower-order modes. Therefore, nanographene exhibits good optical properties due to its low absorption loss. The angles of internal reflection are greater in magnitude than the substrate and cladding key angles. Still, in the tenth TE mode, the internal reflection angles are extremely close to the critical angle as a result of the small substrate decay parameter and the near operating frequency. The tenth TE mode is weakly characterized. The characteristics of TE/TM modes in an asymmetric three-layer slab waveguide structure are realized for various mode orders and various parameters of nanographene material. The field profiles of the TE/TM modes are submitted to comprehend these characteristics.

A novel atmospheric microwave plasma source based on circular waveguide with double ridges for nitrogen fixation

A novel atmospheric microwave plasma source based on circular waveguide with double ridges for nitrogen fixation

A Miniaturized Embedded Frequency Selective Surface‐Based EMI Shield for Microwave Ovens

ABSTRACTThis work presents a new miniaturized frequency selective surface (FSS) design to be employed as an electromagnetic (EM) shield in the 2.45 GHz (ISM band) range, with optically transparent glass substrate. A step‐by‐step procedure on the miniaturization technique and the corresponding frequency response is presented. The proposed FSS layout consists of an optimized square loop and a central reactive element consisting of meandered lines. The metal layout is embedded between borosilicate glass as substrate on top and bottom sides, achieving a final periodicity of 0.12λ. A miniaturization of 69.05% was achieved, and the equivalent circuit model was synthesized to understand the EM behavior of the proposed FSS design, and results were compared. The shielding effectiveness of 53.25 dB was achieved with polarization insensitivity for both TE and TM modes, and the angular stability was also studied. A prototype of the proposed work was fabricated, and the frequency characteristics were studied in the anechoic chamber setup. Ellipsometer setup was used to study the optical properties of prototype, and optical transparency of 81.8% was achieved. The measured and simulated results show close agreement and confirm the usability of the proposed FSS in glass‐based electromagnetic interference (EMI) shielding applications in ISM band.

Wide-band dual-mode adaptive angle anisotropic thermal emitter

The phenomenon of controlling far-field thermal radiation with large-angle emission has gradually attracted attention, but it was previously only present in the TM mode. The ability to make the TE mode have a similar emission trend to the TM mode is important. By introducing a grating-like phase change material:vanadium dioxide (VO2), the emitter has achieved wide-band controllable differences in TE emission rates between the two modes in the atmospheric window range (8–13 um). The range of variation in the emission rate is close to 0.9. Furthermore, temperature-controlled color displays at different angles have been added to the emitter, which makes it easier to judge the working state of the emitter visually. This adjustable broadband large-angle directional emitter makes angle-dependent thermal radiation control possible. It has potential application value in the fields of thermal camouflage, directional radiative cooling, solar cooling waste and heat recovery.

Substrate integrated waveguide differential antenna for full duplex applications

Abstract This paper presents a substrate-integrated waveguide (SIW) differential antenna for full duplex applications. The proposed antenna consists of two square SIW cavities named as outer and inner. The inner cavity is nested into the outer cavity. The outer cavity is differentially excited with a pair of coaxial feed lines, while the inner square patch is orthogonally excited with another pair of differential coaxial feed lines. This orthogonal feeding arrangement results in high isolation between the differential ports. The modified hybrid TE130/310 mode of the outer cavity radiates through a pair of arc-shaped slots at 9.35 GHz, while the TM01 mode of the inner square patch is responsible for the radiations at 8.65 GHz. The proposed antenna prototype is fabricated and measured for validation. Moreover, the designed antenna has a front-to-back ratio better than 22 dB and measured maximum gain values of 6.1 dBi and 7.6 dBi at 8.65 GHz (Port 2 ON) and 9.35 GHz (Port 1 ON), respectively.

Plane wave diffraction by a semi‐infinite parallel‐plate waveguide with partial material loading: The case of H polarisation

AbstractThe analysis of diffraction by a semi‐infinite parallel‐plate waveguide with partial material loading is rigorously carried out using the Wiener–Hopf technique for the H‐polarised plane wave incidence. In solving the Wiener–Hopf equations, the authors apply the Modified Residue Calculus Technique (MRCT) to achieve highly accurate solutions. The scattered field in real space is explicitly derived by performing the inverse Fourier transform of the solution in the transform domain. Within the waveguide, the scattered field is represented in terms of the waveguide TM modes, while the external field is asymptotically evaluated by applying the saddle‐point method to yield a far field expression. The authors present representative numerical examples of the radar cross section for various physical parameters and discuss the far‐field scattering characteristics in detail. Comparisons with the E‐polarisation are also given.

Ultra-broadband absorber and perfect thermal emitter for high-efficiency solar energy absorption and conversion

This study proposes a pyramid-shaped solar absorber designed with multi-layered Ti-SiO2 ring stacked. The structure achieves an average absorption efficiency of 98.03 % over the range of 280–4000 nm, and under AM1.5 spectral conditions, the weighted average absorption efficiency reaches 97.66 %, the bandwidth with an absorption efficiency greater than 90 % reaches 3750 nm. To explore the reason for achieving ultra-broadband absorption with this structure, the electromagnetic field distribution at three absorption peaks was calculated. The results revealed that the resonance between the polarization direction of the three-layer circular ring stacked structure and the plasmon resonance at the junction of Ti and SiO2 contribute to the model's capability for ultra-broadband high-efficiency absorption. At the same time, the thermal emissivity of the structure was calculated at high temperatures of 1000 K and 2000 K, both exceeding 97 %. Furthermore, due to the fully symmetrical design, the absorber is polarization-independent. It was found through calculations that whether in TM mode or TE mode, as the incident angle varies from 0° to 60°, the average absorption efficiency of the absorber changes only by 11.16 %, thereby verifying the structure's excellent insensitivity to incident light angles. In summary, all these characteristics indicate that the model has excellent application prospects in fields such as solar energy collection and photothermal conversion.

Inverse-Designed Ultra-Compact Passive Phase Shifters for High-Performance Beam Steering.

Ultra-compact passive phase shifters are inversely designed by the multi-objective particle swarm optimization algorithm. The wavelength-dependent phase difference between two output beams originates from the different distances of the input light passing through the 4 μm × 3.2 μm rectangular waveguide with random-distributed air-hole arrays. As the wavelength changes from 1535 to 1565 nm, a phase difference tuning range of 6.26 rad and 6.95 rad is obtained for TE and TM modes, respectively. Compared with the array waveguide grating counterpart, the phase shifters exhibit higher transmission with a much smaller footprint. By combining the inverse-designed phase shifter and random-grating emitter together, integrated beam-steering structures are built, which show a large scanning range of ±25.47° and ±27.85° in the lateral direction for TE and TM mode, respectively. This work may pave the way for the development of ultra-compact high-performance optical phased array LiDARs.

Compact Wide‐Stopband QMSIW‐Based BPF for X‐Band Applications

ABSTRACTA novel and compact two‐pole quarter mode substrate integrated waveguide (QMSIW) based bandpass filter with ultra‐wide stopband characteristics (rejection level > 20 dB, up to 4.05f0, where f0 is the center frequency of the bandpass filter) is designed and developed in this paper. The designed second‐order filter comprises of two circular QMSIW cavity resonators. The filter is designed using the dominant TM010 mode of the circular SIW cavity. The TM010 modes of cavities are coupled through the arc‐shaped slot etched in the middle layer. To verify the present design methodology, a second‐order bandpass filter is fabricated and its characteristics are measured. The designed bandpass filter shows outstanding performance in terms of good fractional bandwidth of 14.45%, lower insertion loss of 2 dB and wider stopband behavior (rejection better than 20 dB up to 4.05f0) in a given footprint. The experimental results of the filter matches well the EM‐simulated ones.

Ultrahigh-reflectivity chiral mirrors based on the metasurface of the quarter-waveplate

A study is conducted on a GaAs-based high-contrast subwavelength chiral metasurface (HCCM) designed for 1064 nm. The metasurface integrates a high-contrast subwavelength grating (HCG) for TM mode modulation, a SiO2 support layer, and a compact quarter-waveplate (QWP) to convert linearly polarized light to circularly polarized light. The HCG achieves ultra-high reflectivity at 1064 nm, attributed to the large refractive index contrast between the Si grating and SiO2 layer. The designed HCCM has a reflectivity of more than 99 % for the TM mode and less than 80 % for the TE waves in the wavelength range of 1050 nm–1085nm, and it can also excite the circularly polarized light with an absolute error of less than 0.03 at the transmitting end in the case of the 1064 nm TM wavelength. These results suggest that circular dichroic metasurfaces could offer a promising approach for photonic manipulation in circular polarization VCSELs, potentially reducing the manufacturing challenges and costs associated with traditional methods.

Cavity-based bunch length measurement study for the Super Tau-Charm Facility transport line

In this paper, a nondestructive cavity-based scheme is proposed to achieve high-resolution bunch length measurement in the Super Tau-Charm Facility (STCF) transport line. By extracting the TM010 and TM020 mode signals excited by the beam within a single pillbox cavity, a beam spectrum can be obtained to deduce the Root-Mean-Square (RMS) bunch length. This scheme is more spatially compact compared to the traditional method using double cavities. In this study, the basic principles of the cavity-based bunch length measurement method are explained, the monitor layout is introduced, and the design methods for the cavity and electronics are described. A prototype cavity was machined. Offline tests demonstrate that the eigenmodes in the cavity meet the design requirements and can be used for the bunch length measurements. Based on the online signal characteristics of the Cavity Beam Position Monitors (CBPMs) and the beam parameters of the STCF, the performance of this measurement method is evaluated. For picosecond-level bunches in the STCF transport line, this scheme can provide a bunch length measurement resolution of 233.5 fs at 1.5 nC.

Design of an optically transparent ultrawideband absorber with high angular stability using ITO films.

In this paper, an optically transparency ultrawideband absorber with high angular stability is designed. The proposed absorber is composed of two different materials with indium thin oxide (ITO) conductive films and polydimethylsiloxane (PDMS) substrates. With the aid of a stacked structure design, the absorber has a 90% absorption band from 5 to 43.5 GHz and the fractional bandwidth reaches 158.7%. Also, for the TE mode, the absorption remains stable with the oblique incident angles reaching 50°. And similar angular stability can be observed for the TM mode from 0° to 70°. Besides, the thickness of the absorber is only 0.092 wavelength and transmittance within the visible band is 57.3%. For further verification, a prototype is fabricated and measured. Good agreements between the simulated and the measured results can be observed.

Design of tunable terahertz metamaterial for variable optical attenuation and sensing applications

In this work, an actively tunable terahertz metamaterial (TTM) is proposed to realize variable optical attenuation and sensing applications. The unit cell of TTM is composed of H-shaped resonator (HSR) and C-shaped resonator (CSR). The resonant frequency can be tuned from 0.60 THz to 0.82 THz and show an analog electromagnetically induced transparency (EIT) phenomenon. By adjusting the geometry parameters of HSR and CSR, the enhanced quality (Q) factor is obtained from 2 to 14. Moreover, the CSR can be rotated from 0° to 90° to show the potential in the variable optical attenuator (VOA) application. The resonant intensity at 0.60 THz can be gradually decreased and then disappeared eventually when the CSR rotated from 0° to 90° in TE mode. While the resonant intensity at 0.60 THz can be gradually increased and then reach maximum value from 0° to 90° in TM mode. To demonstrate the proposed TTM can be used for the environmental sensing application, the TTM is exposed on the ambient environment with different refractive indexes from 1.0 to 2.2. The maximum sensitivity is 67 GHz. This work offers a novel approach for the THz metamaterial using for the VOA, optical switching, and sensing applications.

Compact polarization splitter-rotator based on lithium niobate-on-insulator platform

We propose a compact mode-coupled polarization splitter-rotator (PSR) based on the lithium niobate-on-insulator platform. The PSR is composed of an asymmetric directional coupler, a taper, and an S-bend. Cross-polarization mode coupling is achieved using a ridge waveguide and air cladding to break the symmetry of the waveguide cross section with a length of only 61 μm. Simulation results show that the insertion losses of this device in the 1500–1600 nm range are less than 1.85 and 0.31 dB for TM0 and TE0 modes, respectively, and the extinction ratios are more than 22.5 and 22.7 dB, respectively. In addition, the PSR exhibits a polarization conversion efficiency of 99.97% at 1550 nm. The proposed PSR has great potential for applications in polarization-division multiplexing transmitters and on-chip polarization controllers.

Cyclotron resonance imaging at cryogenic temperatures enabled by electric field modification in a microwave cavity

Abstract Cyclotron resonance (CR) is a standard but emerging technique for investigating carrier properties of semiconductors. We have succeeded in CR measurements by employing a microwave cavity designed for electron paramagnetic resonance (EPR). Here, we demonstrate CR imaging to visualize the spatial distribution of carriers at cryogenic temperatures for the first time. To realize CR imaging, it is necessary to account for the electric field modification in the microwave cavity of a cylindrical TM110 mode, which is designed for EPR imaging and is inherently unsuitable for CR measurements. CR detection requires the oscillating electric field perpendicular to the external static magnetic field (B 0) at the sample position, which is not designed for the unloaded cavity. It has been challenging to verify the electric field distribution inside the cavity experimentally, but we show that the observation of the CR signals provides evidence of modification in the electric field. Analysis of the electromagnetic field explains the results, revealing a field distribution whose strength and direction are perturbed due to the lensing effect by the inserted dielectric materials.

Design of a switchable triple-waveguide-based TE-converted polarization beam splitter based on lithium niobate

The lithium-niobate-on-insulator (LNOI) platform has been the new force to drive the developments of integrated photonics, where efficient polarization management and mode conversion are the fundamental issues to be solved. In this work, we proposed a switchable TE-converted polarization beam splitter (PBS) based on optical phase change material (PCM) and a triple-waveguide in simulation. To optimize and analyze the proposed design, the 3D finite difference time domain (3D-FDTD) method is applied in this work. The simulated results indicate that when PCM is in the amorphous state, the device can effectively separate the TM and TE modes, achieving a low insertion loss (<0.5dB) for both modes at 1550 nm. While the PCM is in the crystalline state, the proposed device can realize the efficient conversion from the input TE0 mode to output TE1 mode, which obtains a mode conversion efficiency of 99.5%, crosstalk of −26dB, and insertion loss of 0.5 dB at 1550 nm. We hope such a device can make compact integration and capacity improvement for the integrated photonics in LNOI.

Transverse magnetic supermodes in plasmonic optical fibers excited by radially polarized light.

The overlap integrals method, with a fully vectorial formulation, is used to model the selective excitation of the TM01 mode in a few-mode optical fiber with a radially polarized donut beam, and its coupling to guided modes having a plasmonic character (supermodes). The analyses were performed on a waveguide formed as a step-index few-mode optical fiber coated with a thin gold film, at an operating wavelength of 1310 nm. The waveguide was found to support modes having optical fiber, circular metallic waveguide, and surface plasmon characteristics, depending on geometrical and material parameters. Three purely bound transverse magnetic (radially polarized) supermodes were identified: Two symmetric, labeled sTM01 and sTM02 modes, and one asymmetric, labeled ab mode, where symmetry pertains to the transverse electric field distribution over the gold film. The effective mode indices of the supermodes were studied as a function of the thickness of the gold film and its proximity to the fiber core. Considerations for the selective excitation of the sTM01 mode are discussed along with its possible applications. The transmittance of the supermodes is found to be robust even at sharp waveguide transitions. The results predict that effective excitation of TM supermodes with strong plasmonic character, without significant coupling losses, can be achieved by exciting the fiber with a radially polarized donut beam.

Two-dimensional vector bending sensor based on single excessively tilted fiber grating.

We introduced a two-dimensional vector-bending sensor using excessively tilted fiber grating (ExTFG) encapsulated in a non-neutral axis position within a flexible cylinder. The asymmetrical structure enabled both TM and TE modes of the ExTFG to achieve the competency of one-dimensional vector bending sensing by cleverly leveraging the orthogonal relationship between these modes to achieve the effect of orthogonal cascading of two one-dimensional sensors. The resonance wavelength changes of the TM and TE modes were monitored under equal excitation states to achieve two-dimensional vector bending sensing, which significantly simplified the manufacturing complexity of the sensor; the longer the off-axis distance, the higher the sensitivity, and the smaller the maximum measurable curvature. Through an optimal parameter designation for the sensor, the results showed that the transmission spectra of TM and TE modes varied significantly depending on the curvature and direction of the sensor bending with a maximum sensitivity of -105 pm/m-1 and 105.5 pm/m-1, -70.25 pm/m-1 and 67.5 pm/m-1, respectively. Subsequently, the direction and curvature of the vector bending could be reconstructed using the established algorithm with the measured wavelength shifts of TM and TE modes. The average relative error was about 2.02% for the reconstructed direction angle and about 3.61% for the reconstructed curvature. The proposed sensor offered higher sensitivity than those based on FBGs and improved stability compared to those based on optical fiber interferometers. Therefore, it holds promising applications in structural health monitoring in complex environments and intelligent machinery.