Field In Waveguide Research Articles

Preparation of Novel Heterodimensional Structured Chalcogenide Semiconductor Nano‐Film by Pulsed Laser Deposition Technology

AbstractChalcogenide based nano‐films have attracted considerable attention as a new type of semiconductor material in the fields of optical waveguides, laser devices, and solar cells. However, it remains challenging to use them effectively in a variety of fields, mainly due to their intricate fabrication procedures and limited electrical characteristics. In this study, zinc selenide (ZnSe) is doped with molybdenum (Mo) and gallium (Ga). The heterodimensional structured chalcogenide semiconductor nano‐film is obtained by pulsed laser deposition (PLD). The results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirm that the structure of the nano‐film is compact and the composition is uniformly distributed. The transmittance of all samples is close to 100% in the 400–2000 nm range shown. The P/N type of the film can be controlled by changing the preparation conditions. All the results indicate that the novel heterodimensional structured chalcogenide semiconductor nano‐film in this study has a simple and efficient preparation method, controllable composition, and unique optical/electrical properties. These properties can be used in integrated circuits and photovoltaic power generation.

Direct numerical simulation of acoustic wave propagation in ocean waveguides using a parallel finite volume solver

Numerical simulations based on the Finite Volume Method (FVM) solve the wave equation directly to provide highly accurate predictions of the sound field in ocean waveguides without model simplification and loss of generality. However, the huge computational complexity severely limits the application range of direct numerical solvers for underwater acoustic waves. In this paper, a highly scalable parallel algorithm for solving acoustic models using the cell-centred finite volume method was proposed, and a corresponding direct numerical solver was developed and validated. The paper has three main findings as follows. Firstly, the acoustic solver was implemented based on a generic framework for solving partial differential equations (PDEs), so that more complicated models such as fluid–sound coupling and sound–structure coupling could be easily extended. Secondly, the large spatial scales of underwater sound propagation can be efficiently calculated by parallel computing. Thirdly, our approach demonstrated high computational accuracy and the ability to support complex scenarios. We verify the accuracy and efficiency of the solver through experiments, and prove the solving ability of the solver in large-scale, complex structures and complex configurations.

Attosecond electron microscopy of sub-cycle optical dynamics.

The primary step of almost any interaction between light and materials is the electrodynamic response of the electrons to the optical cycles of the impinging light wave on sub-wavelength and sub-cycle dimensions1. Understanding and controlling the electromagnetic responses of a material2-11 is therefore essential for modern optics and nanophotonics12-19. Although the small de Broglie wavelength of electron beams should allow access to attosecond and ångström dimensions20, the time resolution of ultrafast electron microscopy21 and diffraction22 has so far been limited to the femtosecond domain16-18, which is insufficient for recording fundamental material responses on the scale ofthe cycles of light1,2,10. Here we advance transmission electron microscopy to attosecond time resolution of optical responses within one cycle of excitation light23. We apply a continuous-wave laser24 to modulate the electron wave function into a rapid sequence of electron pulses, and use an energy filter to resolve electromagnetic near-fields in and around a material as a movie in space and time. Experiments on nanostructured needle tips, dielectric resonators and metamaterial antennas reveal a directional launch of chiral surface waves, a delay between dipole and quadrupole dynamics, a subluminal buried waveguide field and a symmetry-broken multi-antenna response. These results signify the value of combining electron microscopy and attosecond laser science to understand light-matter interactions in terms of their fundamental dimensions in spaceand time.

Numerical proposal to solve Maxwell’s equations in a toroidal waveguide

In this contribution, we propose a numerical solution to the Maxwell equations to determine the electromagnetic fields in a toroidal dielectric wave-guide. Analyzing the relationship between the size of the cross-section of the toroid and its bending radius. We considered a sinusoidal time dependence of the electromagnetic field, then we just solve the Helmholtz equation in the waveguide. We propose a numerical way to solve this equation and analyze for to find the power radiation in each synchronous mode. We show a numerical method by calculating the frequencies and the loss factors for any mode in square, triangular, and round waveguides.

Crystal packing and photoelectric property of bis(2-picolyl)amine-functionalized triarylborane and its complexes

Organic crystalline materials are attracting increasing interest due to their promising applications in the fields of nonlinear optics (NLO), organic lasers, optical waveguides, and light-emitting transistors. In this paper, a photoelectric molecule QB was constructed through combining an electron-withdrawing unit, a triarylborane, and a metal-ligand unit of bis(2-picolyl)amine. The crystallization behavior and crystalline photoelectric properties of QB and its complexes were thoroughly studied. This compound exhibited polymorphism, and a green emitting block-like crystal and blue-emission lamellar crystal were obtained, respectively. Their different photoluminescence mechanisms were clarified through X-ray crystallographic analysis and theoretical calculations. Furthermore, the single-crystal structures of the complexes of QB coordinating with KCN and Zn(ClO4)2 were also determined. Crystal QB-KCN emitted strong blue fluorescence at 445 nm, owing to the formation of rigid 2-to-2 adduct, which could effectively suppress non-radiative transitions. Crystal QB-Zn(ClO4)2 showed very weak cyan emission due to its loose molecular packing. The electrochemical results illuminated that the metal coordination can effectively affect the electron-withdrawing ability of conjugated triarylborane, and further affect the monomolecular luminescent properties due to the intramolecular charge transfer. We believe that polymorphism and metal coordination are available means to obtain excellent crystalline photoelectric materials.

Use of Interference Patterns to Control Sound Field Focusing in Shallow Water

The possibility of controlling localized fields in multimode shallow water waveguides based on the principle of interference invariance was studied. Within the framework of the numerical experiments in a wide frequency range of 100–350 Hz and range intervals of 10–100 km, the possibilities of focusing the sound field by wavefront reversal and controlling of the focusing of the focal spot by frequency tuning in shallow water waveguides was analyzed. The focal spot scanning was carried out by frequency tuning with a fixed distribution of the sound field at receiving and transmitting vertical antenna apertures. A comparative analysis of the features of focusing and focal spot control for summer and winter stratification of the water layer was carried out. It is shown that the parameters of the focal spot during frequency tuning were more stable in the winter waveguide. It is demonstrated that the sound frequency tuning had a piecewise continuous character and was carried out on a domain of one continuous track and jump-passing on the other track in accordance with the waveguide interference fringes in the range–frequency domain.

Millimeter-Wave Near-Field Evaluations of Polylactic Acid (PLA) Filament Used in Polymer-Based Additive Manufacturing (AM)

ABSTRACT Additive manufacturing (AM) remains to be a rapidly growing industry with applications that are extended beyond metals and to other materials, such as polymers, ceramics, and concrete, to name a few. However, advancement in the development of inspection techniques, particularly in-line nondestructive testing (NDT) methods, lags significantly. Most of the research in developing such methods has focused on metal-based AM. This paper investigates the efficacy of three high-resolution near-field millimeter-wave probes for detecting small voids in the feedstock polymeric filaments used for AM. The electromagnetic (EM) design and optimization of these probes are discussed in this paper. The design of the probes is based on concentrating the interrogating electric field of an open-ended waveguide in a small region corresponding to the area of a thin dielectric slab insert. This results in achieving a higher spatial resolution than when using only the open-ended waveguide. Extending the dielectric slab to an optimum value out of the waveguide makes the electric field more concentrated and potentially further improves the spatial resolution. These modifications also reduce the detection sensitivity as a function of increasing standoff distance. However, the spatial resolution of these probes varies more rapidly as the standoff distance increases. Subsequently, the efficacy of these three probes was studied and compared using a comprehensive set of numerical EM simulations at V-band (50–75 GHz). Afterward, three such probes were fabricated, at V-band (50–75 GHz), and were used to measure the reflection responses of the stock Polylactic Acid (PLA) filaments with a very small hemispherical surface void. Root-Mean-Squared-Error (RMSE), between reference and defective filaments and over the simulated and measured frequency range, was calculated as a criterion to compare the detection capability of the three probes in the entire frequency band. The results showed that at V-band (50–75 GHz) the spatial resolution of the standard open-ended rectangular waveguide is deemed sufficient detecting small surface voids of the stock PLA filaments.

An Accurate and Numerically Stable Formulation for Computing the Electromagnetic Fields in Uniform Bend Rectangular Waveguides

This article describes a numerically stable formulation for the analysis of electromagnetic fields in rectangular cross section waveguides with a curved longitudinal axis. A novel set of scaled Hankel functions for real-valued arguments and complex-valued orders is introduced for rescaling the characteristic equations associated with the transverse electric (TE) and magnetic (TM) fields of the exact boundary value problem. The exponentially scaled cylindrical functions presented here prevent numerical underflow and overflow errors associated with large real and large imaginary orders without sacrificing accuracy. The proposed methodology is validated against variable-precision arithmetic (VPA) results. Numerical results are also presented for waveguides with large radii of curvature, where the present methodology is compared with perturbation ones in several examples. Dielectric-filled waveguides with small radii of curvature are investigated, and our solutions are compared with finite-integration technique (FIT) results.

Modal structure of the sound field in a shallow-water waveguide with a gassy sediment layer: Experiment and theory

Motivated by a series of experiments in the Lake Kinneret (Israel), the paper investigates low-frequency sound propagation in the three-layer model of the shallow water waveguide, where a thin layer of gas-saturated sediment is situated between a homogeneous fluid sub-bottom and a continuously stratified water column. Typical values of the thickness and sound speed in the gassy layer are 1 m and 250 m/s. The layer is thin compared to typical water depth of about 40 m. Normal mode structure of the acoustic field is analyzed. It is shown that with increasing frequency each normal mode transforms into a mode trapped in the gassy layer. These modes have unusually small phase and group speeds that are significantly less than the sound speed in water. Theoretically predicted normal mode dispersion curves are compared to the dispersion curves retrieved from observations of shipping noise. Phase speeds of normal modes are measured by cross-correlatingthe noise recorded on two sparse vertical arrays. A technique is proposed for solving the inverse problem of determining the parameters of a gas-saturated layer by matching the measured and modeled frequency dependencies of the normal mode phase speed.

ELF-EM fields in the multi-layer spherical ‘Earth-ionosphere’ model based on WKB

Abstract With a high signal-to-noise ratio and a great depth of exploration, the wireless electromagnetic method (WEM) has wide applications in the exploration of deep mineral resources and oil and gas reservoirs. Extremely low-frequency electromagnetic (ELF) waves emitted from a horizontal antenna are used to achieve synchronous acquisition for different receivers of multi-coverage information in a global region. However, previous research based on a planar model ignored the curvature of the Earth. This work focuses on the electromagnetic fields (EM fields) in the model of a spherical ‘Earth ionosphere’ to extend the coverage of WEM. By transferring the EM fields from a vertical electric dipole (VED) as well as a vertical magnetic dipole (VMD) in the multi-layered medium of the Earth, we obtain the formulae for the EM fields emitted by a horizontal electric dipole (HED) by using a reciprocity theorem. The correctness of the proposed method is verified by comparing it with the approximate analytical formula and previous work. Based on the above results, we have studied the propagation and frequency characteristics of electromagnetic fields in a spherical waveguide consisting of the ionosphere and earth. The results show that the electromagnetic fields under the spherical model produce interference effects that are different from those of the planar model. The electromagnetic response of the layered Earth was then discussed, and its potential as an electromagnetic technique for exploring the deep Earth was demonstrated.

Investigation of resonant mode and simultaneous excitation of multiple modes in slot‐coupled rectangular dielectric resonator antenna for multiband applications

AbstractA low‐profile rectangular dielectric resonator antenna (RDRA) through the slot‐based feed method is studied for the multiband operation. Based on the perfect magnetic wall (PMW) model and dielectric waveguide model (DWM), field distributions and resonant frequencies of the RDRA intrinsic modes are calculated for multimodal analysis. The microstrip backed slot coupling scheme is employed for the simultaneous excitation of multiple modes. A prototype is fabricated and validated. By generating 10 modes simultaneously including TEy111 to TEy711, and TEx221 to TEx421 modes. The RDRA is able to provide good multiband performance.

Влияние неоднородной теплозащиты на характеристики излучения антенны космического аппарата

Introduction: Knowledge of the electrical characteristics of the onboard antenna on the trajectory of the descent of the spacecraft makes it possible to assess the presence or absence of radio communication. Under conditions of aerodynamic heating, the thermal protection of the onboard antenna heats up unevenly in thickness and becomes electrically inhomogeneous. Purpose of the work: Determination of the radio technical characteristics of the onboard antennas of the returning spacecraft with the effect of high-temperature heating on the thermal protection of the antenna based on calculations using the developed mathematical model of the antenna with thermal protection. Methods: Expressions for the structure of the radiation field of a rectangular waveguide under the above conditions were derived by the WKB method. Of the well-known analytical methods of solution, it is possible to use the method of integral transformations and the method of eigenfunctions. Both of these methods were used in this work. Results: The obtained theoretical results are new, they allow predicting the radio technical characteristics of the onboard antenna, taking into account uneven heating across the thickness of the thermal protection at low temperature gradients. A mathematical model of the spacecraft's onboard antenna on the descent trajectory has been developed, taking into account the inhomogeneity of thermal protection under conditions of aerodynamic heating. Practical significance: The development of a mathematical model of the main radio technical characteristics of onboard antennas, taking into account the impact of high-temperature aerodynamic heating, as well as the results of numerical calculations, can be applied in the development of recommendations for choosing thermal protection and recommendations for reducing the effect of temperature changes in the electrical parameters of thermal protection on the characteristics of onboard antennas and reducing time loss of radio communication or loss recovery.

Thermal diffusion coupling mechanism and its application of discrete waveguide

For discrete optical systems integrated into optical fibers, the optical fields of the individual waveguides are coupled and correlated with each other. This paper studies how to adjust the refractive index of discrete waveguides by thermal diffusion, so as to enhance the coupling between discrete waveguides, and also constructs the discrete waveguide thermally diffused model and the thermally diffused coupling model of twin-core and three-core fibers. The multicore fiber is heated different times by a hydrogen-oxygen flame, and the outgoing light field at the end face of the optical fiber is monitored at the same time. Then, the three-dimensional refractive index measurement results of the thermally diffused multicore fiber verify the feasibility of thermal diffusion technology to change the refractive index of discrete waveguides for coupling. Thermal diffusion technology can be used to fabricate multicore fiber couplers. By combining multicore fiber and core-by-core inscribed fiber Bragg grating technology and by using thermal diffusion technology, the single-channel sensing measurement can be realized. The method of changing the refractive index of discrete waveguides through thermal diffusion has the advantages of high integration, high stability, and mass fabrication. The research on the thermal diffusion of discrete waveguides can improve the application potential of multicore fiber sensing systems, and promote the broad application of discrete waveguide structure optical fiber in the fields of optical communication, optical sensing, biomedicine, and artificial intelligence.

Parallel numerical simulation of weakly range-dependent ocean acoustic waveguides by adiabatic modes based on a spectral method

With the increasing demand for underwater detection, interest in the acoustic field of range-dependent ocean waveguides is also growing. For weakly range-dependent ocean waveguides, adiabatic modes represent a compromise between accuracy and computational cost and occupy an important place in the simulation of numerical sound fields. However, either existing adiabatic-mode programs consider too few layers of media or the root-finder tends to miss roots. In addition, none of the programs can solve the acoustic field excited by a line sound source located anywhere in the plane. In this paper, we first derive an expression for the acoustic field excited by a line source by adiabatic modes and then introduce a high-precision spectral method to solve the local eigenmodes. For the lower boundary condition of the acoustic half-space, we use the eigenvalue transformation technique to transform the transcendental algebra system formed by spectral discretization into a generalized eigenvalue problem. Several representative numerical experiments are designed to verify the accuracy of the algorithm. After analyzing the parallelism, the multiprocess and multithread hybrid strategy is adopted to further accelerate the algorithm in parallel, and parallel numerical simulation is carried out on the Tianhe–2 multicore supercomputer; favorable acceleration is achieved.

Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

Most traditional sound field calculation methods regard the seabed as the horizontal stratified liquid sea bottom and conduct simulation analysis based on the frequency domain. Hence, the generality of the above research methods is limited to varying degrees. To accurately clarify the propagation characteristics and mechanism of very low‐frequency (VLF, ≤100 Hz) sound waves in the shallow sea, a numerical calculation model is established using the finite element time‐domain method (FETD) based on the three‐dimensional cylindrical coordinate system. Using this model, the effects of sea‐bottom topographies and geoacoustic parameters on the composition and characteristics of VLF sound fields in the shallow sea and their corresponding mechanism are investigated through the comparative analysis of various numerical simulation examples. The simulation results demonstrate that the low‐frequency sound field in the full waveguide of the shallow sea is composed of normal mode waves in the seawater layer, Scholte waves at the liquid‐solid interface, and elastic waves at the sea bottom. Compared with the soft sea bottom, which has a more negligible elastic impedance, the hard sea bottom is more conducive to the long‐distance propagation of normal mode waves and the excitation of Scholte waves. The Scholte waves on the hard sea bottom are significantly stronger than those on the soft sea bottom. Compared with the horizontal sea bottom, the uphill topography enhances the sound energy leakage to the sea bottom. It is more favorable to receive Scholte waves at shallow depths, whereas the influence laws of downhill topography are the opposite.

High-Resolution and Broadband Two-Stage Speckle Spectrometer

Motivated by handheld optical sensing applications, spectrometers with small footprint, broadband operating bandwidth, and low cost are highly desired. In this paper, we propose and experimentally test a fully integrated high-resolution and broadband two-stage spectrometer based on a multimode waveguide (MMW). MMW was used to enhance the resolution of the system while the integrated photodiodes provide a fully integrated solution. Six waveguide modes were launched into the multimode waveguide via asymmetric directional couplers and each mode could be individually enabled via its respective optical switches. The output mode field of the multimode waveguide was spatially sampled by six integrated photodiodes. Switch arrays increase the physical channels from 6 to 384 possible states (2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> switch states × 6 detectors), therefore significantly enhance the bandwidth. Using compressive sensing algorithms, 5000 spectral channels of the optical signal can be reconstructed which is an order of magnitude higher than the cutting edge method. We measured the spectrometer to have a spectral resolution of 0.02-nm and optical bandwidth of 100 nm. Both the sparse and continuous spectra were reconstructed successfully.

Environmental Monitoring: A Comprehensive Review on Optical Waveguide and Fiber-Based Sensors.

Globally, there is active development of photonic sensors incorporating multidisciplinary research. The ultimate objective is to develop small, low-cost, sensitive, selective, quick, durable, remote-controllable sensors that are resistant to electromagnetic interference. Different photonic sensor designs and advances in photonic frameworks have shown the possibility to realize these capabilities. In this review paper, the latest developments in the field of optical waveguide and fiber-based sensors which can serve for environmental monitoring are discussed. Several important topics such as toxic gas, water quality, indoor environment, and natural disaster monitoring are reviewed.

Anisotropy influence on guided wave scattering for composite structure monitoring

Composite structures are widely used for aerospace applications but are prone to barely visible impact damage from low velocity impacts. Guided wave measurements using sparse arrays of distributed sensors provide an important structural health monitoring (SHM) tool for detecting and localizing impact damage in composites. However, the anisotropy of composites needs to be considered as it can affect guided wave propagation and scattering, impacting imaging performance. Improved defect characterization can be achieved by considering the scattering characteristics for the signal processing. Scattering around two different damage types for multiple incident wave directions in a quasi-isotropic carbon fiber reinforced polymer (CFRP) panel were investigated. Full 3D Finite Element (FE) simulations were compared to the measured scattered guided wave field at an artificial insert delamination. Permanent magnets mounted on an undamaged region of the plate were used as scattering targets and both numerical and experimental scattering patterns were compared to the delamination results. Strong directional dependency was observed for both damage types, with energy focusing along the fiber directions of the outer ply layers. For the delamination, mostly forward scattering is observed for all incident wave directions, whereas the magnet blocked forward wave transmission and scattered wave energy in all directions. 2D scattering matrices were calculated, demonstrating distinct scattering behavior for each damage type. Implications of anisotropy and angular scattering on SHM guided wave sparse array imaging are discussed.

Research on the Range-Frequency Interference Characteristics of Target Scattering Field in a Shallow Water Waveguide

Based on the target scattering model and the normal mode theory in a shallow water waveguide, a mathematical model of the acoustic intensity under the coupling condition of the target and the environment was deduced, and the interference striations in the monostatic and bistatic configuration were obtained by simulations. Further, a field experiment was carried out in a lake, and the data were collected for a spherical target in two frequency bands, i.e., 20−40 kHz and 40−80 kHz. The experiment results showed good agreement with the simulations. The results of the simulation and the experiment showed that the existence of the target made the interference phenomenon in shallow water waveguides more complex, and the range-frequency interference characteristics were closely related to the configuration of the sonar system, the target scattering function, the frequency range, and the target movement trajectory. These interference phenomena were found and theoretically analyzed in the paper. The research results can be applied to target detection and recognition, signal parameter estimation, target tracking, and other fields.

Directed self-assembly of organic crystals into chip-like heterostructures for signal processing

Organic single crystals show broad application prospects in the field of optical confinement and waveguides due to their low optical transmission loss and tunable optical properties. Individual one- or two-dimensional (1D or 2D) optical waveguide crystals have the limitations of a single function in organic photonics. In this work, a chip-like organic heterostructure was fabricated using an elaborately designed, sequential growth method. By regulating the concentration of each organic component, the processes of solution self-assembly, etching, and epitaxial self-assembly are successively performed to complete the directional growth of organic micro/nanostructures. Notably, the as-prepared chip-like organic heterostructure is composed of 1D/2D optical waveguide crystals, which can realize multidimensional photon transportation and multi-terminal directional optical signal output. Furthermore, the unique 2D optical waveguide properties of the chip-like heterostructures offer opportunities for constructing the encoding form of the output optical signal at the micro/nanoscale.