Behavior Of Waveguides Research Articles

A spectral element-based reduced order model for thermoacoustic stability analysis in waveguides

A novel approach to perform linear stability analysis using a spectral element-based reduced order model is proposed, thereby facilitating the comprehensive study of (thermo)acoustic (in)stability across complex waveguide configurations. Providing a generalization of a wave-based method (e.g. spectral element method) to the Laplace domain, this study is offering not only a new methodology for analyzing thermoacoustic systems but also expanding the application of the spectral element method and other wave-based techniques to a broader class of problems. By solving the wave equation in the Laplace domain, spectral elementary matrices can be defined in the complex plane in both wavenumber and frequency domains, allowing for an examination of system stability. This technique supports a wide range of waveguide investigations, whether using an analytical description to get the spectral matrix or a numerical method to determine the dispersion curves and eigenvectors in the cross-section. Additionally, the proposed method simplifies the implementation of parametric optimization procedures due to its low computational cost, thus offering significant advancements in the study of waveguide behavior of thermoacoustic systems.

Directional self-assembly of organic vertically superposed nanowires

Organic crystal-based superimposed heterostructures with inherent multichannel characteristics demonstrate superior potential for manipulating excitons/photons at the micro/nanoscale for integrated optoelectronics. However, the precise construction of organic superimposed heterostructures with fixed superimposed sites remains challenging because of the random molecular nucleation process. Here, organic vertically superimposed heterostructures (OSHs) with fixed superimposed positions are constructed via semi-wrapped core/shell heterostructures with partially exposed cores, which provide preferential nucleation sites for further molecular epitaxial growth processes. Furthermore, the relative length ratio from 21.7% to 95.3% between interlayers is accurately adjusted by regulating the exposed area of the semi-wrapped core/shell heterostructures. Significantly, these OSHs with anisotropic optical characteristics demonstrate well regulation of excitation position-dependent waveguide behaviors and can function as photonic barcodes for information encryption. This strategy provides a facile approach for controlling the nucleation sites for the controllable preparation of organic heterostructures and advanced applications for integrated optoelectronics.

Flexural wave propagation in canonical quasicrystalline-generated waveguides

We investigate the propagation of harmonic flexural waves in periodic two-phase phononic multi-supported continuous beams whose elementary cells are designed according to the quasicrystalline standard Fibonacci substitution rule. The resulting dynamic frequency spectra are studied with the aid of a trace-map formalism which provides a geometrical interpretation of the recursive rule governing traces of the relevant transmission matrices: the traces of three consecutive elementary cells can be represented as a point on the surface defined by an invariant function of the square root of the circular frequency, and the recursivity implies the description of a discrete orbit on the surface. In analogy with the companion axial problem, we show that, for specific layouts of the elementary cell (the canonical configurations), the orbits are almost periodic. Likewise, for the same layouts, the stop-/pass-band diagrams along the frequency domain are almost periodic. Several periodic orbits exist and each corresponds to a self-similar portion of the dynamic spectra whose scaling law can be investigated by linearising the trace map in the neighbourhood of the orbit. The obtained results provide a new piece of theory to better understand the dynamic behaviour of two-phase flexural periodic waveguides whose elementary cell is obtained from quasicrystalline generation rules.

On the role of geometric phase in the dynamics of elastic waveguides.

The geometric phase provides important mathematical insights to understand the fundamental nature and evolution of the dynamic response in a wide spectrum of systems ranging from quantum to classical mechanics. While the concept of geometric phase, which is an additional phase factor occurring in dynamical systems, holds the same meaning across different fields of application, its use and interpretation can acquire important nuances specific to the system of interest. In recent years, the development of quantum topological materials and its extension to classical mechanical systems have renewed the interest in the concept of geometric phase. This review revisits the concept of geometric phase and discusses, by means of either established or original results, its critical role in the design and dynamic behaviour of elastic waveguides. Concepts of differential geometry and topology are put forward to provide a theoretical understanding of the geometric phase and its connection to the physical properties of the system. Then, the concept of geometric phase is applied to different types of elastic waveguides to explain how either topologically trivial or non-trivial behaviour can emerge based on the geometric features of the waveguide. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'.

Wave Propagation for Structural Health Monitoring (WaveProSHM): open software with GUI

Guided wave–based SHM methods have been explored extensively in recent decades. The wave propagation modelling including piezoelectric transducers and various damage types helps understand intricacies of guided wave behavior and for designing a robust SHM system. However, modelling aspects are still challenging. Moreover, commercially available software for the modelling of guided waves often lacks appropriate high-order elements and code optimization for fast GPU computations. This research aimed to develop and disseminate to the SHM community the open software based on highly efficient vectorised code of the time domain spectral element method which can be run on GPU. The developed code is written in MATLAB with Graphical User Interface (GUI) and communicates with GMSH – open source finite element mesh generator. It can model signals of propagating guided waves in structures which are excited and registered by an array of piezoelectric transducers. The capabilities of the software are shown in an example of a large-scale problem of interacting guided waves with delamination.

A study on attenuation patterns of acoustic waves in waveguide structures with flexural boundaries

This research article investigates the attenuation patterns of acoustic waves within waveguide structures featuring flexural boundaries. By employing advanced methods in vibrations and controls, the study aims to enhance our understanding of waveguide behavior and offer valuable insights for optimizing acoustic wave propagation in diverse applications. The entire waveguide structure is tuned through cooperative interactions involving elastic plates, membranes, and rigid boundary surfaces. The lower boundary of the expansion chamber consists of a rigid plate, with elastic membranes covering the upper surfaces of the cavity. The problem is formulated in terms of transmission and reflection coefficients of the modes, enabling the solution of the scattering problem. Matching acoustic pressure and velocity at the waveguide junction yields the scattering coefficients. The results reveal that the scattering coefficients are intricately influenced by both the geometric characteristics of the waveguide and the frequency of the incident waves. Notably, the first higher-order mode of the cut-off frequency of the waveguide structure corresponds to the frequency at which the dissipation coefficient reaches its maximum value. This research provides valuable insights into the scattering behavior of acoustic waves in waveguide configurations, contributing to the design of acoustic devices and systems. Rigorous support and justification for all aspects of the mode-matching method, including pressure and velocity matching, eigen properties, physical edge conditions, convergence criteria, and energy conservation, are provided through thorough algebraic and numerical analyses, confirming the validity of the solution methodology.

Dynamic Dipole Moment of Luminescent Liquid Crystals Enabled Highly Efficient Active Waveguide Materials Design and Synthesis

AbstractOrganic optical waveguide materials have attracted considerable attention for their promising applications in photonic and optoelectronic devices. However, for most materials, excellent light‐loss properties at high temperature cannot be obtained due to many factors. Consequently, realizing efficient optical waveguide materials that perform well at elevated temperatures remains a significant challenge. In this study, relying on the luminescent properties and self‐assembly properties of luminescent liquid crystals (LLCs), successfully fabricated materials are present for highly efficient active optical waveguides. A systematically synthesized set of LLCs with different structures is named according to the substituent type and the position of the cyano group, namely α‐DECN, α‐DEEOCN, β‐DECN, and β‐DEEOCN. Notably, α‐DECN and β‐DECN reveal hexagonal columnar phase, while α‐DEEOCN and β‐DEEOCN exhibit smectic phase. Optical waveguide experiments have revealed that the obtained LLCs showed highly efficient optical waveguide behavior, where the lowest light loss reached 0.15 dB mm−1 at room temperature. Remarkably, these LLCs show even lower light loss at high temperatures, with the light loss reaching 0.11 dB mm−1 as the lowest point. Further experimental results indicate that this phenomenon is attributed to the change in the dipole moment of these molecules. This research forms a significant groundwork for advanced exploration in optical waveguide material.

Slab waveguide communication study using Finite Difference Method (FDM) with fourth-order compact scheme

An accurate and efficient semi-vectorial mode solver, examining Electric (E) and Magnetic (H) fields, is utilized to explore the communication characteristics of various slab waveguides. This approach relies on the Finite Difference Method (FDM) using uniform grid points, employing a Higher (Fourth) Order Compact type technique coupled with Conjugate Gradient (CG) iteration. The present study is an extension of the previous work where various aspects of E- and H-field propagations through rib-strucured waveguide was analyzed successfully. By incorporating the refractive index profile of the slab structure, excellent functionality of the waveguide is demonstrated here in Electric field by utilizing the concepts of normalized index and effective or modal index, confinement factor, and the modal birefringence properties which proves to be critical for potential applications in photonic integrated circuits. The materials chosen for the purpose are AlGaAs-GaAs and GeSi which play a vital role in characterizing the waveguides’performances through simulation using MATLAB. The use of surface and contour plots aids in visualizing the distribution of corresponding field within the guided modes. This analysis significantly contributes in understanding the waveguide's behavior and confinement capability during the field propagation. Most importantly, the variations of the waveguides’performance indices with their structure parameters help to identify their optimized values for fabrication to enhance the transmission efficiency of the waveguide.

Analytical investigations of propagation of ultra-broad nonparaxial pulses in a birefringent optical waveguide by three computational ideas

This paper mainly concentrates on obtaining solutions and other exact traveling wave solutions using the generalized G-expansion method. Some new exact solutions of the coupled nonlinear Schrödinger system using the mentioned method are extracted. This method is based on the general properties of the nonlinear model of expansion method with the support of the complete discrimination system for polynomial method and computer algebraic system (AS) such as Maple or Mathematica. The nonparaxial solitons with the propagation of ultra-broad nonparaxial pulses in a birefringent optical waveguide is studied. To attain this, an illustrative case of the coupled nonlinear Helmholtz (CNLH) system is given to illustrate the possibility and unwavering quality of the strategy utilized in this research. These solutions can be significant in the use of understanding the behavior of wave guides when studying Kerr medium, optical computing and optical beams in Kerr like nonlinear media. Physical meanings of solutions are simulated by various Figures in 2D and 3D along with density graphs. The constraint conditions of the existence of solutions are also reported in detail. Finally, the modulation instability analysis of the CNLH equation is presented in detail.

Self-assembled D–π–A multifunctional systems with tunable stimuli-responsive emission and optical waveguiding behaviour

Crystalline assembly of naphthalenimide derivatives with a D–π–A structure gives rise to light guiding and mechanical and thermal stimuli-responsiveness.

Analyzing monopole sources modeling with structural variations and material contrast: An analytical perspective

This study presents a comprehensive analysis of modeling acoustic radiation from monopole sources within waveguides, considering variations in structural parameters, including backward passage and the use of sound-absorbent materials. The investigation employs analytical techniques, including mode-matching methods and Fourier transforms, to address the intricate boundary value problem governing acoustic behavior in waveguides. Eigenfunction expansions are utilized to describe acoustic responses in various segments, leading to systems of linear algebraic equations that are numerically solved after truncation. The research examines the influence of critical factors such as frequency, thickness of absorbent materials, and chamber length on power components, including reflection, absorption, transmission, and propagation, across different regions of the waveguide. Notably, the choice of sound-absorbent material emerges as a significant factor affecting scattering characteristics, with A-Glass outperforming E-Glass and Steel Wool in various scenarios. These insights offer valuable knowledge for optimizing acoustic systems in engineering applications, facilitating the design and enhancement of sound control mechanisms within waveguides.

Design and optical waveguide behavior of full-color emitting materials with adjustable band gap

Optical waveguide materials that span the entire visible spectrum is paramount for the efficacious operation of photon transmission devices in many contexts. Notably intriguing is the use of manipulating the band gap to finely modulate chromatic diversity within the luminous material. In this context, we synthesized three distinct organic small molecules, employing carbazole's inherent proclivity as the electron donor, while engaging thiophene, pyrimidine, and fluorenone as adept electron acceptor moieties. Evidently, our investigation unveiled a remarkable metamorphosis in the emitted fluorescence, wherein the chromatic spectrum transitions from blue to green, and subsequently to orange, as the electron acceptor group's capacity for electron absorption diminishes. Interestingly, the three materials manifest an inherent propensity for facile preparation into one-dimensional nanostructures, characterized by smooth surfaces, concurrently exhibiting commendable performance as optical waveguides. Our findings deepen a comprehensive understanding of the design of materials with the full visible spectrum, which might lead to innovations in the design of photonic integrated structures.

Organic Bilayer Heterostructures with Built-In Exciton Conversion for 2D Photonic Encryption.

Organic multilayer heterostructures with accurate spatial organization demonstrate strong light-matter interaction from excitonic responses and efficient carrier transfer across heterojunction interfaces, which are considered as promising candidates toward advanced optoelectronics. However, the precise regulation of the heterojunction surface area for finely adjusting exciton conversion and energy transfer is still formidable. Herein, organic bilayer heterostructures (OBHs) with controlled face-to-face heterojunction via a stepwise seeded growth strategy, which is favorable for efficient exciton propagation and conversion of optical interconnects are designed and synthesized. Notably, the relative position and overlap length ratio of component microwires (LDSA /LBPEA = 0.39-1.15) in OBHs are accurately regulated by modulating the crystallization time of seeded crystals, resulting into a tailored heterojunction surface area (R = Loverlap /LBPEA = 37.6%-65.3%). These as-prepared OBHs present the excitation position-dependent waveguide behaviors for optical outcoupling characteristics with tunable emission colors and intensities, which are applied into two-dimensional (2D) photonic barcodes. This strategy opens a versatile avenue to purposely design OBHs with tailored heterojunctions for efficient energy transfer and exciton conversion, facilitating the application possibilities of advanced integrated optoelectronics.

Homogeneous and Heterogeneous Self‐Assembly of Luminescent Pyromellitic Dianhydride‐Based Charge‐Transfer Complexes

AbstractUsing easily hydrolyzable brominated pyromellitic dianhydride (PMDA) as an electron acceptor, a wide variety of structurally stable binary organic charge‐transfer (CT) microcrystals that are stabilized by dominant intermolecular CT interactions is achieved. By varying the electron‐donating abilities of π‐electron compounds, the resulting single crystalline CT assemblies display tailorable fluorescence emissions spanning from green to near‐infrared. Upon implantation of a π‐electron donor anthracene (An) into fluoranthene‐PMDA (Fl‐PMDA), red and NIR emissions of ternary alloyed assemblies are substantially enhanced due to efficient energy transfer from Fl‐PMDA to An‐PMDA as well as structural complementarity between two CT complexes. Depending on the well‐matched epitaxial relationship, seeded growth of phenanthrene‐PMDA (Ph‐PMDA) onto the pre‐existing An‐PMDA microcrystals is also achieved, leading to core‐shell heterostructures with full and partial coverage. Such an epitaxial growth strategy is also applicable to the construction of microscale heterostructures of diverse CT complex combinations. The ternary Fl1−xAnx‐PMDA alloyed assemblies display composition‐dependent tailorable optical waveguiding behaviors. While An‐PMDA@Ph‐PMDA core‐shell microrods present wavelength‐dependent two‐photon excited fluorescence performances. The rational creation of these homogeneous and heterogeneous CT‐assembled architectures provides us a deep insight to investigate multicomponent functional organic cocrystals.

Arbitrary Phase Optimization Through Adaptively-Scheduled Nanophotonic Inverse Design

Design of integrated photonic devices continues to drive innovation in electro-optical systems for many applications ranging from communications to sensing and computing. Traditional design methods for integrated photonics involve using fundamental physical principles of guided-wave behavior to engineer optical functionalities for specific application requirements. While these traditional approaches may be sufficient for basic functionalities, the set of physically realizable optical capabilities these methods remains limited. Instead, photonic design can be formulated as an inverse problem where the target device functionality is specified, and a numerical optimizer creates the device with appropriate geometrical features within specified constraints. However, even with inverse design methods, achieving arbitrarily-specified phase offsets on-chip remains an important problem to solve for the reliability of interferometry-based nanophotonic applications. In order to address difficulties in achieving simultaneous phase and power optimization in inverse nanophotonic design, in this paper, we develop a set of optimization approaches that can enable user-specified phase differences in single-wavelength and multi-wavelength nanophotonic devices. By specifying phase offset targets for each output, we prevent convergence failures resulting from the changes in the figure of merit and gradient throughout the iterative optimization process. Additionally, by introducing phase-dependent figure of merit terms through an adaptive scheduling approach during the optimization, we accelerate device convergence up to a factor of 4.4 times. Our results outline a clear path towards the optimization of nanophotonic components with arbitrary phase-handling capabilities, with potential applications in a wide variety of integrated photonic systems and platforms.

Analytical Model of Guided Waves in Periodically Perforated Dielectric Structure and Its Applications to Terahertz Substrate-Integrated Image Guide (SIIG)

This article presents and derives an analytical model for accurately analyzing lossy dielectric waveguides in the THz regime. By considering the dielectric loss of waveguides and applying the impedance boundary condition (IBC), the proposed method can accurately simulate the waveguiding behavior. By applying the Fourier series expansion along with the Floquet theory, an analytical model is developed, which can effectively account for periodic perforations, which describes an inherent feature of substrate-integrated dielectric waveguides at THz frequencies. The applicability and high accuracy of the proposed method are demonstrated by providing several examples and comparisons with measurements from a fabricated prototype. The efficiency of the proposed method in terms of simulation runtime is compared with some commercial EM software packages. These results demonstrate that while the proposed method maintains a minimum accuracy of 95% compared with the CST Studio Suite and Ansys HFSS software, the simulation runtime is reduced by 300 times.

Tunable elastic wave modulation via local phase dispersion measurements of a piezoelectric metasurface with signal correlation enhancement

Tunable piezoelectric metasurfaces have been proposed as a means of adaptively steering incident elastic waves for various applications in vibration mitigation and control. Bonding piezoelectric material to thin structures introduces electromechanical coupling, enabling structural dynamics to be altered via tunable electric shunts connected across each unit cell. For example, by carefully calibrating the inductive shunts, it is possible to implement the discrete phase shifts necessary for gradient-based waveguiding behaviors. However, experimental validations of localized phase shifting are challenging due to the narrow bandgap of local resonators, resulting in poor transmission of incident waves and high sensitivity to transient noise. These factors, in combination with the difficulties in experimental circuitry synthesis, can lead to significant variability of data acquired within the bandgap operating region. This paper presents a systematic approach for extracting localized phase shifts by taking advantage of the inherent correlation between the incident and transmitted wavefronts. During this procedure, matched filtering greatly reduces noise in the transmitted signal when operating in or near bandgap frequencies. Experimental results demonstrate phase shifts as large as −170° within the locally resonant bandgap, with an average 28% reduction in error relative to a direct time domain measurement of phase, enabling effective comparison of the dispersive behavior with corresponding analytical and finite element models. In addition to demonstrating the tunable waveguide characteristics of a piezoelectric metasurface, this technique can easily be extended to validate localized phase shifting of other elastic waveguiding metasurfaces.

On application of the new mapping method to magneto-optic waveguides having Kudryashov’s law of refractive index

This paper obtains solitons and other exact traveling wave solutions to magneto-optic waveguides that maintains Kudryashov’s law of refractive index using the new mapping method and computer algebraic systems (CAS) such as Maple or Mathematica. These solutions are important for understanding the behavior of waveguides in telecommunications, optical computing and sensing. Dark solitons, bright solitons, bright-dark solitons, combo solitons, singular solitons and periodic solutions are obtained. Further, some 2D and 3D graphs of the obtained exact traveling wave solutions are shown. Finally, comparison between our new results and the well-known results is made.

Donor-Acceptor-Donor 1H-Benzo[d]imidazole Derivatives as Optical Waveguides.

A new series of donor-acceptor-donor (D-A-D) structures derived from arylethynyl 1H-benzo[d]imidazole was synthesized and processed into single crystals with the goal of testing such crystals' ability to act as optical waveguides. Some crystals displayed luminescence in the 550-600 nm range and optical waveguiding behavior with optical loss coefficients around 10-2 dB/μm, which indicated a notable light transport. The crystalline structure, confirmed by X-ray diffraction, contains internal channels that are important for light propagation, as we previously reported. The combination of a 1D assembly, a single crystal structure, and notable light emission properties with low losses from self-absorption made 1H-benzo[d]imidazole derivatives appealing compounds for optical waveguide applications.

Growth of single-crystals and microstructures using benzothiadiazole derivatives for efficient optical waveguide and nonlinearity

Organic nanomaterials have been extensively studied for the applications of the electronic and photonic fields. The bottom-up fabrication through self-assembly provides a powerful strategy to construct the nanostructures. In this work, we synthesized a conjugated molecule, namely, 4-(1-phenyl-1H-1,2,3-triazol-4-yl)benzo[c][1,2,5]thiadiazole (BT-SC), based on benzothiadiazole and benzene moieties bridged by a triazole. Then, a simple solvent-vapor annealing technique was presented to drive the self-assembly of BT-SC into highly uniform microrods or microfibers. The morphology of the self-assembly could be controlled by simply changing the solution concentration. The compound also could be assembled into aligned nanowires by wetting into hard templates of anodic aluminum oxide (AAO). The fabricated microrods showed strong emitter and excellent optical waveguide behaviors excited with a UV laser. Moreover, the microrods displayed nonlinear optical responses of two-photon excited fluorescence and could therefore become building blocks for actual photonic devices.