Order TE Research Articles

Evaluation of the effectiveness of energetic thermal electrons on the excitation of the ionospheric red 6300 Å airglow

In this paper we use previously calculated ionosphere electron temperatures Te in order to estimate the 6300 Å (red) airglow intensity enhancements attributed to thermal electrons from the tail of a Maxwellian electron distribution of sufficiently increased electron temperature. Then, we compare our results with the relevant observed measurements and we comment on the quality of the comparison and the possible causes of the differences. We also calculate the airglow intensity characteristic rise and decay times and compare them to the experimental ones, and we investigate the origin of the electrons which excite the red airglow. In the end, we assess the departure of the ionosphere electron energy distribution from a purely Maxwellian one, and the role of the electron elastic and inelastic collisions with the other components of the ionospheric F-region.

Ultra‐wideband directional electrically small antenna for UHF through C‐band 5G and beyond 5G applications

AbstractA semi‐spherical combined transverse electromagnetic (TEM) horn and loop antenna is designed for directional ultra‐wideband operation from 0.42 to 6 GHz for 5G and beyond 5G applications across military and commercial sectors. The antenna structure fits within a sphere with 3‐cm radius, thus operating as electrically small over the lower part of the band (ka = 0.5 at 0.795 GHz and ka = 1 at 1.59 GHz). To spread the currents across the volume while maintaining the required relationship between the lowest order TE and TM modes, the loop section is modified to conform with the enclosing minimum sphere. The TEM horn, bowtie, and resistive loading are then tuned to achieve improvement over the conventional topology in the radiation efficiency by >7% when ka = 0.5 and >22% when ka = 1.

Optoelectronic properties fine-tuning through chalcogenide-based π-bridge for dye molecules featuring hydantoin anchoring group: first-principle calculations

This study investigates the effect of chalcogenides and electron-withdrawing groups CN and F on the optoelectronic properties using DFT and TD-DFT methods, with a focus on the use of a hydantoin anchoring group as an alternative to carboxylic acid-based groups. The results show that the studied dyes have a planar structure that facilitates intramolecular charge transfer and that propeller-shaped terminal phenyl rings help reduce dye aggregation. The maximum absorption was observed between 485 and 627 nanometres, and bathochromic shifts in UV-Vis spectra were observed in the order NH, S, O, Se, and Te for both F- and CN-containing dyes. Excited-state lifetime was highest for dyes containing heavier chalcogenides. Adsorption energies of the dye onto TiO2 anatase (101) with 3 × 6 supercell were found in the range of 0.13–0.79 eV and 0.61–1.54 eV for CN and F-containing dyes, respectively. Dyes featuring Se and Te exhibit superior properties for dye-sensitized solar cell application, and chalcogenide-based dyes are worthy of experimental synthesis. Overall, the study provides valuable insights into the optoelectronic properties of dyes and their potential use in more efficient solar cell technologies.

Broadband and low-loss TM-pass polarizer using tilted subwavelength structures

Photonic systems built on the Silicon-on-Insulator platform exhibit a strong birefringence, and must thus be operated with a single polarization for most applications. Hence, on-chip polarizers that can effectively suppress an undesired polarization state are key components for these systems. Polarizers that extinguish TE polarized light while letting TM polarized light pass with low losses are particularly challenging to design for the standard 220 nm Silicon-on-Insulator platform, because the modal confinement is stronger for TE polarization than for TM polarzation. Here, we propose and design a broadband, low loss and high extinction ratio TM-pass polarizer by engineering a Bragg grating that reflects the fundamental TE mode into the first order TE mode using a subwavelength metamaterial which at the same time allows the TM mode to pass. Our device achieves an extinction ratio in excess of 20 dB, insertion losses below 0.5 dB and back-reflections of the fundamental TE mode of the order of -20 dB in a bandwidth of 150 nm as demonstrated with full 3D-FDTD simulations.

Compact nonvolatile 2×2 photonic switch based on two-mode interference.

On-chip nonvolatile photonic switches enabled by phase change materials (PCMs) are promising building blocks for power-efficient programmable photonic integrated circuits. However, large absorption loss in conventional PCMs (such as Ge2Sb2Te5) interacting with weak evanescent waves in silicon waveguides usually leads to high insertion loss and a large device footprint. In this paper, we propose a 2×2 photonic switch based on two-mode interference in a multimode slot waveguide (MSW) with ultralow loss Sb2S3 integrated inside the slot region. The MSW supports two lowest order TE modes, i.e., symmetric TE00 and antisymmetric TE01 modes, and the phase of Sb2S3 could actively tune two-mode interference behavior. Owing to the enhanced electric field in the slot, the interaction strength between modal field and Sb2S3 could be boosted, and a photonic switch containing a ∼9.4 µm-long Sb2S3-MSW hybrid section could effectively alter the light transmission between bar and cross ports upon the phase change of Sb2S3 with a cross talk (CT) less than -13.6 dB and an insertion loss (IL) less than 0.26 dB in the telecommunication C-band. Especially at 1550 nm, the CT in the amorphous (crystalline) Sb2S3 is -36.1 dB (-31.1 dB) with a corresponding IL of 0.073 dB (0.055 dB). The proposed 2×2 photonic switch is compact in size and compatible with on-chip microheaters, which may find promising applications in reconfigurable photonic devices.

Design of Filtering Dielectric Resonator Antenna Arrays Using Simple Feeding Networks

A 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 filtering dielectric resonator antenna (DRA) array is investigated in this communication. The central DRA is excited by a microstrip-coupled slot, while the two side DRA elements are, respectively, excited by the central DRA via a low-profile patch-loaded dielectric bridge laid between them. In order to integrate the filtering function, the open stub of the microstrip feed line is elaborately designed to generate a radiation null at the upper band edge, while two vertical metallic strips are added onto the sidewalls of the central DRA to provide another radiation null at the lower band edge. On the other hand, in order to achieve an enhanced gain in the operating passband, the higher order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">113</sub> mode of the DRA elements is excited. It is found that due to the loading effects of metallic patches and conformal strips, three stepping resonances of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">113</sub> mode are generated in the passband, leading to a wide impedance bandwidth of 13.7% and a stable gain of 11.4 dBi. As a result, both good radiation and filtering performance are achieved without requiring complex filtering circuits. To demonstrate the extensibility of the array, a larger 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 filtering DRA array with a high peak gain of 14.7 dBi is further designed by just using a three-way power dividing network.

Numerical analysis of a grating embedded bidirectional integrated optical coupler pressure sensor.

A numerical analysis of a grating embedded bidirectional optical coupled waveguide structure is presented for the first time, to our knowledge. A finite difference method (FDM) based scheme is devised to extract the allowed eigen TE and TM modes of the structure. Sensing characteristics of the grating employed between two high refractive index couplers are then explored. The influence of strain on the composite structure is numerically analyzed for better understanding of guiding phenomena. A numerical method based on a three-point central finite difference scheme with proper boundary conditions at the point of discontinuity is developed. For an accurate sensitivity analysis, a large number of mesh points (N=1000) are used in the FDM algorithm, while the whole analysis is done on MATLAB software. To the best of the authors' knowledge, Bragg grating sensitivities of individual TE and TM modes have been estimated for the first time. It is found that higher order TE and TM modes show improved sensitivity performance. The physics behind the improved sensitivity of the proposed structure is correlated with existing cases. The proposed technique is based on effective refractive index theory, and hence it is easy to implement. This work can be easily extended to obtain temperature, humidity, and vibration sensitivities of other novel structures.

A chemical model to predict the formation of a semiconductor solid solution: New insights in the use of bulk and surface mechanochemical reactions

A chemical model capable of predicting the formation of a semiconductor solid solution, via high-energy milling of powder precursors, is proposed. According to experimental findings provided by X-ray powder diffraction and X-ray photoelectron spectrometry, the model encompasses three major stages related to a series of oxygen levels, which are function of oxygen potential during milling. The initial step involves the formation of oxide mixtures, as evidenced by oxidizing highly reactive chalcogens (Se and Te) and re oxidation of PbO. In the middle step, which represents the largest process stage, Te or Se share electrons to act as Te (IV) and Se (IV) in order to form Pb complex chalcoxides. The formation of high purity Pb2SeTe semiconductor solid solution is detected at the final stage, in such stage the chalcogens act as reducing agents. Consequently, neither inert nor high vacuum atmospheres are required during the milling process. The model involves a quaternary interpretation whose predictions are validated with experimental findings, theoretical, and even analogous phases not reported so far in literature.

Uniform Auxiliary Space Preconditioning for HDG Methods for Elliptic Operators with a Parameter Dependent Low Order Term

The auxiliary space preconditioning (ASP) technique is applied to the hybridizable discontinuous Galerkin (HDG) schemes for three different elliptic problems with a parameter dependent low order te...

Mode hybridization analysis in thin film lithium niobate strip multimode waveguides

Mode hybridization phenomenon in air-cladded X-cut Y-propagating and Z-propagating thin film lithium niobate strip multimode waveguides is numerically studied and a mathematical relation between structural parameters leading to hybrid modes is formulated. Dependence of hybrid modes on waveguide dimensions, sidewall angles and wavelength is also analyzed. The results obtained are used to design lithium niobate on insulator (LNOI) taper for converting fundamental TM mode to higher order TE mode, and an optimum length for achieving a high conversion efficiency of 99.5% is evaluated. Birefringent Y-propagating LN and isotropic Z-propagating LN tapers are compared in terms of length, figures of merit, and fabrication tolerance. Tapers exhibit a broad bandwidth of 200 nm with an extinction ratio less than − 18 dB. The results of mode hybridization analysis are useful in design optimization of adiabatic tapers, tunable time delays, optical interconnects, mode converters and demultiplexers for mode division multiplexing (MDM) applications.

Mode conversion characteristics of multimode magneto-optical Bragg diffraction cells

We study the dependence of magneto-optical (MO) coupling coefficients on the modal fields for the design of multi-mode MO Bragg cells. The mode conversion and diffraction efficiencies between the same order TM and TE modes can theoretically be up to about 98% by adjusting the excitation frequency of the fundamental-mode magneto-static forward volume wave (MSFVW) in the bismuth-substituted yttrium iron garnet film at the optimized thickness and length. The different order mode conversion is also available by means of the higher-mode MSFVWs. The resulting mode conversion-based switch function is discussed.

A novel dual resonance long period waveguide grating based highly sensitive refractive index sensor with reduced temperature sensitivity

In this paper, we are proposing a novel structure to reduce the temperature cross sensitivity of a refractive index (RI) sensor based on dual resonance long period waveguide grating in a metal clad ridge waveguide, operating near the dispersion turning point. The core of the waveguide is considered to be made of two parts having opposite thermo-optic coefficients with grating written in one part only. Considering the coupling between the fundamental TE mode and a higher order TE mode, we have shown that by adjusting the thickness of the two parts of the core, it is possible to achieve blueshifts for both the resonance wavelengths with the increase in temperature unlike the case of a conventional dual resonance spectrum where two resonance wavelengths show opposite shifts. As a result, an extremely low temperature cross sensitivity ∼0.006 nm/0C has been achieved, whereas the dual resonance spectrum holds its conventional behavior with the change in ambient RI, showing an extremely high RI sensitivity ∼57,260 nm/RIU near water RI 1.33. Further, it has been observed that as we approach the dispersion turning point, temperature sensitivity decreases gradually whereas RI sensitivity increases, leading to a more accurate ambient RI measurement

Generalized Multimode SIW Cavity-Based Sensor for Retrieval of Complex Permittivity of Materials

In this paper, the generalized substrate integrated waveguide (SIW) cavity technique is presented for the retrieval of broadband complex permittivity of medium loss dielectrics using a number of higher order modes of the proposed cavity. The proposed SIW cavity design improves the coupling by implementing a novel feeding topology to achieve a better quality factor for the higher order TE $_{10n}$ modes as compared with the conventional SIW feeding arrangement. The conventional SIW cavity perturbation formula is modified to overcome various limitations of the SIW topology, such as the lower $Q$ -factor, lower sample to cavity volume ratio, and larger frequency shifts observed for the higher order modes. The applicability of the proposed technique is first numerically validated using independent data obtained with the help of full-wave electromagnetic solver, and then, the accuracy is compared with various cavity-based techniques available in the literature. Finally, the proposed SIW cavity sensor is fabricated on Rogers’ RT5880 substrate, where a number of standard RF substrates are tested using the network analyzer. The proposed generalized scheme based on the improved SIW cavity provides reasonably accurate values of the complex permittivity of the medium-loss dielectric substrates at multiband of microwave frequency in the range of 10–20 GHz.

Ultrahigh-sensitive temperature sensor based on modal interference in a metal-under-clad ridge waveguide with a polymer upper cladding.

We propose a highly sensitive temperature sensor based on modal interference in a metal-under-clad ridge waveguide (MUCRW) with polydimethylsiloxane as the upper cladding. The proposed sensor exploits the interference between the fundamental and the first higher order TE modes of the MUCRW. The increased fractional modal power in the ambient medium due to the metal under-cladding along with the high thermo-optic coefficient of the upper cladding results in a very significant change in the modal characteristics of the two interfering modes with temperature variation. Moreover, the effect of temperature change is more pronounced for the higher order mode compared with the fundamental mode, resulting in an ultrahigh sensitivity of the modal interference to the ambient temperature. The sensitivity of the proposed sensor structure is found to be as high as 8.35 nm/°C, which, to the best of our knowledge, is the highest reported sensitivity in any integrated optic waveguide-based temperature sensor.

Diagnostics of high-temperature plasmas by the X-ray spectra of heavy elements

Modified comparison method is developed. In this method detailed theoretical calculations of spectra of heavy elements is conducted varying one parameter ( Te ) in order to find the most complete matching of the structure of the theoretical and the experimental Mo spectra in laser-produced plasmas.

In-plane rotation of the doubly coupled photonic crystal nanobeam cavities

In this letter, a nano-electro-mechanical-systems (NEMS) mechanism is proposed to drive the in-plane rotation of the doubly coupled photonic crystal (PhC) nanobeam cavities. The corresponding interactions between optical resonances and rotations are investigated. This is the first in-plane rotational tuning of the PhC cavities, which benefits from the flexible design of NEMS actuators. In experiments, more than 18 linewidths of the third order TE even mode corresponding to 0.037 mrad of the shrinking angle between the two nanobeam cavities are demonstrated; this study provides one more mechanical degree of freedom for the practical optomechanical interactions.

The role of Te(IV) and Bi(III) chloride complexes in hydrothermal mass transfer: An X-ray absorption spectroscopic study

Tellurium (Te) and bismuth (Bi) are two metal(loid)s often enriched together with gold (Au) in hydrothermal deposits; however the speciation and transport properties for these two metals in hydrothermal systems are poorly understood. We investigated the effect of chloride on the speciation of Te(IV) and Bi(III) in hydrothermal solutions using in-situ XAS spectroscopy.At ambient temperature, oxy-hydroxide complexes containing the [TeO3] moiety (e.g., H3TeO3+ under highly acidic conditions) predominate in salty solutions over a wide range in pH and salt concentrations. Te(IV)–Cl complexes only appear at pH25°C≤2 and high Cl− activity (≥10). The highest order Te(IV) chloride complex detected is TeCl4(aq), and contains the [TeCl4] moiety. Upon heating to 199°C, the Te(IV)–Cl complexes become more stable; however they still required highly acidic conditions which are likely to exist only in very limited environments in nature.At ambient temperature, Bi(III) is coordinated to 5.5(5) Cl atoms in high salinity, acidic (HCl≥0.5m) chloride solutions. This, combined with large EXAFS-derived structural disorder parameters, suggests that the Bi(III) complex is most likely present as both BiCl52− and BiCl63−. The number of Cl atoms coordinated to Bi(III) decreases with increasing temperature; at around 200°C and above, Bi(III) is coordinated to three Cl atoms.Overall the data show that Te(IV) chloride complexes can be ignored in predicting Te mobility under oxidizing conditions in most geological environments, but that Bi(III) chloride complexes are expected to account for Bi mobility in acidic brines. New thermodynamic properties for Bi(III) chloride complexes are provided to improve reactive transport modeling of Bi up to 500°C. Although higher order complexes such as BiCl52− and BiCl63− exist at ambient temperature, the BiCl3(aq) complex becomes the predominant chloride complex in saline solutions at T≥200°C.

Tunable fiber polarizing filter based on a single-hole-infiltrated polarization maintaining photonic crystal fiber

A tunable fiber polarizing filter based on selectively filling a single hole of a solid-core polarization maintaining photonic crystal fiber with high index liquid are proposed and demonstrated. Two groups of polarization-dependent resonance dips in the transmission spectrum of the single-hole-infiltrated photonic crystal fiber are observed. Theoretical and experimental investigations reveal that these resonant dips result from the couplings between the silica core fundamental mode at x or y polarization and high order modes (TM(01), TE(01) and HE(11)) in the liquid core. Especially, a distinctive characteristic near the strongest resonant point (SRP) is demonstrated and revealed. The transmission loss and spectral shape at the SRP wavelength are extremely sensitive to the filling length and temperature (or Refractive Index, RI), which permits a fiber bandpass or bandstop polarizing filter with a good performance on tunability and controllability. Furthermore, the narrowband dips on both sides of the SRP wavelength have wavelength-dependent tuning velocities, providing a method to achieve flexible and controllable filters as well as two- or multi-parameter sensors with a compact structure.

Hydrogen Production from Water Vapor Plasmolysis Using DBD-Corona Hybrid Reactor

Hydrogen is produced by plasmolysis of (1) demineralized water vapors (steam) and (2) water vapor and argon gas. In the current study, a custom-made dielectric barrier discharge (DBD)-corona hybrid reactor has been designed and used for steam plasmolysis. The objective is to show the feasibility of hydrogen production from water vapor plasmolysis at atmospheric pressure at a relatively smaller interelectrode distance and to characterize the plasma for its fundamental properties. The generated plasma properties have been characterized by applying spectrometric analysis, in which the measured plasma temperatures are demonstrated in the order Te > Texc > Trot, which confirms the nonlocalized thermal equilibrium (LTE) existence in the plasma bulk. Moreover, the estimated electron number density (1.765 × 1017 m–3) shows an exceptional energy for water vapor dissociation, which eventually results in a reasonable efficiency. The estimated energy efficiency and thermodynamic efficiency for water vapor plasmolysis along with steam was found to be 78.8% and 79.2%, respectively. Accordingly, the calculated production rate (20 g/kWh) and the predicted cost (£0.09/kWh) are shown to be competitive to the electrolysis process, which is increasingly applied for hydrogen production, with the benefit of reduced equipment size and low power consumption.

Mode-evolution-based polarization rotator-splitter design via simple fabrication process

A mode-evolution-based polarization rotator-splitter built on InP substrate is proposed by combining a mode converter and an adiabatic asymmetric Y-coupler. The mode converter, consisting of a bi-level taper and a width taper, effectively converts the fundamental TM mode into the second order TE mode without changing the polarization of the fundamental TE mode. The following adiabatic asymmetric Y-coupler splits the fundamental and the second order TE modes and also converts the second order TE mode into the fundamental TE mode. A shallow etched structure is proposed for the width taper to enhance the polarization conversion efficiency. The device has a total length of 1350 µm, a polarization extinction ratio over 25 dB and an insertion loss below 0.5 dB both for TE and TM modes, over the wavelength range from 1528 to 1612 nm covering all C + L band. Because the device is designed based on mode evolution principle, it has a large fabrication tolerance. The insertion loss remains below 1 dB and the polarization extinction ratio remains over 17 dB with respect to a width variation of +/- 0.12 µm at the wavelength of 1570 nm, or +/- 0.08 µm over the entire C + L band.