We analytically solve the guided transverse magnetic modes of symmetrical planar slot waveguides and show that multiple modes may exist in a slot waveguide. For all types of modes in waveguides with the index of the s...
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We analytically solve the guided transverse magnetic modes of symmetrical planar slot waveguides and show that multiple modes may exist in a slot waveguide. For all types of modes in waveguides with the index of the slot greater than that of the cladding and vice versa, field solutions and characteristic equations are derived and the cutoff conditions are provided and discussed. (C) 2015 Optical Society of America
The existence of frequency stop-bands, in which transmission of the vibro-acoustic energy is impossible, suggests that the periodic structures may be used for vibro-isolation. In any technical application, however, on...
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The existence of frequency stop-bands, in which transmission of the vibro-acoustic energy is impossible, suggests that the periodic structures may be used for vibro-isolation. In any technical application, however, only a finite segment of such a structure can be used. This paper is concerned with comparison of the eigenfrequency spectra of finite periodic structures with location of stop-bands for their infinite counterparts. A hierarchy of four mathematical models is considered. In each case, special attention is paid to eigenfrequencies and eigenmodes of a single periodicity cell with appropriate boundary conditions. The influence of the amount of periodicity cells in a finite compound structure on its eigenfrequency *** is analyzed. Several features common for the considered models are found and discussed in the context of the existing knowledge on the subject. (C) 2015 Published by Elsevier Ltd.
A novel method based on waveguide modal analysis is presented to evaluate the effectiveness in terms of frequency bandgaps of bounded periodic metamaterials. The effect of the size of the bounded medium, i.e., the num...
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A novel method based on waveguide modal analysis is presented to evaluate the effectiveness in terms of frequency bandgaps of bounded periodic metamaterials. The effect of the size of the bounded medium, i.e., the number of periodic unit cells, on the frequency bandgaps predicted by Floquet-Bloch theory in the infinite case is investigated and quantified. The waveguides considered in this work have a bounded cross-section and an infinite longitudinal axis simulated by Perfectly Matched Layers. Its useful area is made of a bounded 1D or 2D -periodic matrixinclusion metamaterial. In the 2D -periodic case, an approach combining the waveguide modal analysis with the Floquet-Bloch transform is further proposed. Applying the proposed method, the SH-waves propagating in a waveguide are studied by using the finite element method. The discrete spectrum of the waveguide and the associated attenuated or trapped wave modes are calculated and analyzed, which provides, within a semi -analytic framework, an exact characterization regarding the attenuation coefficient and the frequency bandgaps of the studied bounded periodic medium. More particularly, effectiveness indicators are defined to compare the width and the position of frequency bandgaps between the bounded and infinite cases as a function of the cell number. Last but not least, the proposed method is also successfully applied to bounded periodic media with local resonators to characterize their filtering and attenuation effectiveness, which shows its interest in such a case of great practical interest.
Abundant seismic waveforms have been collected in Xinjiang since 2007, following the deployment of permanent stations by the China National Seismic Network and the Xinjiang Seismic Network. We investigated regional at...
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Abundant seismic waveforms have been collected in Xinjiang since 2007, following the deployment of permanent stations by the China National Seismic Network and the Xinjiang Seismic Network. We investigated regional attenuation of the S-Lg phase in the crustal waveguide and site response in Xinjiang using broadband recordings at 44 stations from 118 earthquakes with magnitudes of 4.4-7.0 occurring in Xinjiang and adjacent areas between January 2009 and February 2022. We used linear regression analysis of the Fourier acceleration amplitude spectra in 18 frequency bands from 0.1 to 24.86 Hz to estimate site response terms and distance-dependent anelastic attenuation quality factor Q in the crustal waveguide at regional distances. The regression site terms of stations located in the Tarim and Junggar Basins show significant amplification at low frequencies and strong attenuation at higher frequencies due to the presence of thick sedimentary deposits. We quantified the linear behavior of the logarithms of the high-frequency site terms versus frequency using the zero distance attenuation parameter kappa 0 (Anderson and Hough, 1984). A positive correlation was observed between kappa 0 and the thickness of the sedimentary layers in Xinjiang. We observed some consistent patterns in the behavior of the site response terms as a function of sediment thickness over the frequency range of 0.1-24.86 Hz. Linear functions of sediment thickness were used to model the site response in Xinjiang at each of the 18 frequencies. An alternative approach that adopted the kappa 0 model as a function of sediment thickness can be used to estimate site responses at high frequencies ( >= 5.66 Hz). The results of this study demonstrate the nature of site effects on earthquake ground motions caused by the thick sedimentary deposits in Xinjiang and provide a preliminary site response model as a function of sediment thickness for this region.
We studied generalized Bloch boundary conditions and their finite element implementation within the theoretical framework of a symmorphic space group. By combining translation symmetry operations with mirror and rotat...
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We studied generalized Bloch boundary conditions and their finite element implementation within the theoretical framework of a symmorphic space group. By combining translation symmetry operations with mirror and rotational symmetry operations, we developed a procedure for implementing generalized Bloch boundary conditions in the finite element method (FEM) for periodic photonic structures. First, we lay out the theoretical foundation and numerical implementation of generalized Bloch boundary conditions in FEM. We illustrate the proposed method via 2D/3D periodic photonic structures. Without a loss of generality, we calculate the band structures of 2D/3D photonic crystals using our proposed generalized Bloch boundary conditions and benchmark the results against the conventional Bloch boundary conditions. The comparisons show that band structure and eigenmode yield excellent agreement with the results obtained from conventional Bloch boundary conditions. However, our method has improved the computational efficiency by at least twofold. We further elaborate the comparisons with computation errors, memory efficiency, and computation times, all of which show that our proposed method outperforms the conventional one due to careful consideration of the mirror and rotational symmetry operation, apart from the translation symmetry. In addition, our method can easily be extended to other methods such as FDTD and transfer matrix. (c) 2024 Optica Publishing Group
Thin films and ridge waveguides based on large-diameter semiconducting single-wall carbon nanotubes (s-SWCNTs) dispersed in a polyfluorene derivative are fabricated and optically characterized. Ridge waveguides are de...
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Thin films and ridge waveguides based on large-diameter semiconducting single-wall carbon nanotubes (s-SWCNTs) dispersed in a polyfluorene derivative are fabricated and optically characterized. Ridge waveguides are designed with appropriate dimensions for single-mode propagation at 1550 nm. Using multimode ridge waveguides, guided s-SWCNT photoluminescence is demonstrated for the first time in the near-infrared telecommunications window.
In this paper, based on a new treatment for local base transformation, a modified operator marching method is provided to accurately compute optical propagation in the inhomogeneous waveguide terminated by a perfectly...
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In this paper, based on a new treatment for local base transformation, a modified operator marching method is provided to accurately compute optical propagation in the inhomogeneous waveguide terminated by a perfectly matched layer. Compared with the adjoint operator method (AOM), high-precision results of the optical propagation can be obtained in numerical simulations, which demonstrate that the new treatment is much better than the AOM. This technique is helpful to optimize the designs of the optical waveguides and the integrated optics devices. (C) 2015 Optical Society of America
The characteristics of guided modes in circular waveguides of a uniaxial anisotropic chiral core and a cladding filled with anisotropic plasma are presented. The cladding region is assumed to be infinitely extended wi...
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The characteristics of guided modes in circular waveguides of a uniaxial anisotropic chiral core and a cladding filled with anisotropic plasma are presented. The cladding region is assumed to be infinitely extended with an external applied magnetic field oriented along the direction of propagation in the waveguide. The characteristics equation for the modes in this waveguide are obtained. The variations of the propagation properties with the plasma parameters, chiral parameters, and the cyclotron frequency of plasma have been investigated. Particularly, the effects of the chirality and the cyclotron frequency of plasma on the magnitude and orientation of the energy flux of the guided modes for three kinds of uniaxial anisotropic chiral media have been numerically investigated. Comparisons of the computed results of the presented formulations with published results for some special cases confirm the accuracy of the presented analyses.
We studied the influence of temperature increase to 1500 degrees C on ultrasound absorption at frequencies from 0.1 to 1.0 MHz in tungsten, molybdenum, vanadium, graphite, and fused silica. The ultrasound absorption c...
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We studied the influence of temperature increase to 1500 degrees C on ultrasound absorption at frequencies from 0.1 to 1.0 MHz in tungsten, molybdenum, vanadium, graphite, and fused silica. The ultrasound absorption coefficient in these materials was calculated. It was shown that the fused silica has the smallest ultrasound absorption coefficient for temperatures up to 1000 degrees C. Vanadium and graphite also have small values of this coefficient for the considered temperature. The ultrasound absorption was investigated experimentally in graphite and fused silica waveguides. We demonstrated that the ultrasound absorption did not change in graphite with the temperature increase, but it increased in fused silica by a factor 2 for the temperature above 1000 degrees C. We show that different acoustical and mechanical properties of vanadium, graphite, and fused silica allow using them for waveguide applications and buffer rods in crystal growth at temperatures below 1500 degrees C and ultrasound frequency below 1.0 MHz. (C) 2015 Elsevier B.V. All rights reserved.
This work presents a deep neural network (DNN)-based approach for identifying the modal field distributions of closed non-radiating waveguides. Specifically, physics-informed neural networks (PINNs) are used to solve ...
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This work presents a deep neural network (DNN)-based approach for identifying the modal field distributions of closed non-radiating waveguides. Specifically, physics-informed neural networks (PINNs) are used to solve the Helmholtz partial differential equation. The PINN architecture includes incorporation of boundary conditions and selection of initial conditions to obtain required modes inside the waveguides. In this paper, furthermore, the use of this method is illustrated for waveguides consisting of inhomogeneous and anisotropic media, where we apply a domain decomposition-based deep learning method. Our approach successfully identifies all eigenmode distributions with an error of less than -12 dB as compared to analytical and full-wave simulation results. Notably, we further enhance the efficiency of our approach by utilizing transfer learning, achieving a 23 times reduction in solution time. Our results demonstrate PINNs as an alternative to traditional methods in accurately calculating waveguide modal field distributions and its applicability to other partial differential equation based EM problems.
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