The Maxwell system is considered in a three-dimensional domain G having several cylindrical ends. The coefficients are variable and stabilizing at infinity with exponential rate. The limit coefficients are independent...
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The Maxwell system is considered in a three-dimensional domain G having several cylindrical ends. The coefficients are variable and stabilizing at infinity with exponential rate. The limit coefficients are independent of the axial coordinate in the corresponding cylinder. A scattering matrix is defined on the waveguide continuous spectrum outside of the thresholds. The matrix depends on the spectral parameter, is of finite size, which remains constant between neighbouring thresholds and changes when the parameter crosses a threshold. The scattering matrix is unitary. In the paper, we propose a method for approximate computation of the scattering matrix. Moreover, we prove the existence of finite one-side limits of this matrix at every threshold.
waveguides consisting of artificial media based on periodic structures at the subwavelength scale are a major open topic in contemporary applied physics and engineering. Recent research efforts focus on the properties...
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waveguides consisting of artificial media based on periodic structures at the subwavelength scale are a major open topic in contemporary applied physics and engineering. Recent research efforts focus on the properties of guided modes in artificial structures. However, as the cornerstone of applications, matching techniques between these interesting waveguides and traditional waveguides deserve more attention. We report a broadband adiabatic mode-matching technique for efficient coupling between conventional microwave transmission lines (a coplanar waveguide and a slotline) and one-dimensional (1D) interface waveguides consisting of transverse-electric (TE) and transverse-magnetic (TM) artificial impedance surfaces. The transverse electromagnetic (TEM) mode is adiabatically transformed to the line wave mode at the 1D impedance-interface. Proposed matching techniques open up avenues for applications of various impedance-interface waveguides.
Nanoscale oscillators based on the spin-transfer torque effect are attractive candidates for the hardware implementation of neural networks using an array of coupled oscillators. Here, we demonstrate that the mutual c...
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Nanoscale oscillators based on the spin-transfer torque effect are attractive candidates for the hardware implementation of neural networks using an array of coupled oscillators. Here, we demonstrate that the mutual coupling through rf strip lines can be used for synchronizing two spin-torque nano-oscillators (STNOs). Using the current nanotechnology, it is feasible to design asymmetric coupling between two STNOs via this scheme, which would mimic many biological neural networks. A unique feature of our experiment is that we can characterize the synchronized state by varying the phase as well as the strength of the coupling, going into the nonlinear regime.
Spectrum is a basic dimension of waves ranging from electromagnetic to acoustic waves where information can be encoded and multiplexed. The manipulation of the sound spectrum is desirable in applications of acoustic c...
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Spectrum is a basic dimension of waves ranging from electromagnetic to acoustic waves where information can be encoded and multiplexed. The manipulation of the sound spectrum is desirable in applications of acoustic communication and voice encryption, which, however, is challenging to realize. Here, based on temporally modulated waveguides, we create effective gauge fields to generate frequency domain Bloch oscillations (FBOs) to control the spectrum of sound. The modulation can induce mode transitions in the waveguide band and form a discrete frequency lattice where the wave vector mismatch during transitions acts as an effective electric field that drives FBOs. Furthermore, we find the modulation phase accompanying transitions serves as an effective gauge potential that can control the initial oscillation phase. We report that multiple FBOs with judiciously designed oscillation phases can be further cascaded to realize acoustic spectrum reconstruction, unidirectional transduction, and bandwidth engineering. This study reveals the significance of gauge fields in FBOs and functionalizes its cascaded configurations for advanced control of the sound spectrum. This paradigm may find versatile applications in acoustic secure communication, information encryption, and processing.
The interplay of photon spin and orbital angular momentum (OAM) in the optical fiber (one-dimensional waveguide) has recently risen to the forefront of quantum nanophotonics. Here, we introduce the fermionic dual of t...
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The interplay of photon spin and orbital angular momentum (OAM) in the optical fiber (one-dimensional waveguide) has recently risen to the forefront of quantum nanophotonics. Here, we introduce the fermionic dual of the optical fiber, the Dirac wire, which exhibits unique electronic spin and OAM properties arising from confined solutions of the Dirac equation. The Dirac wires analyzed here represent cylindrical generalizations of the Jackiw-Rebbi domain wall and the minimal topological insulator, which are of significant interest in spintronics. We show the unique longitudinal spin arising from electrons confined to propagation in a wire, an effect which is fundamentally prohibited in planar geometries. Our work sheds light on the universal spatial dynamics of electron spin in confined geometries and the duality between electronic and photonic spin.
The realization of all-optical AND logic gates for pulsed signal operation based on the photonic bandgap transmission phenomenon is proposed. We are using realistic planar air-hole type coupled photonic crystal wavegu...
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The realization of all-optical AND logic gates for pulsed signal operation based on the photonic bandgap transmission phenomenon is proposed. We are using realistic planar air-hole type coupled photonic crystal waveguides (C-PCWs) with Kerr-type nonlinear background medium. The novelty of our analysis is that the proposed AND logic gate operates with the temporal solitons, which maintain a stable envelope propagating in the nonlinear C-PCWs, enabling true ultrafast full-optical digital signal processing in the time-domain. The bandgap transmission takes place when the operating frequency is chosen at the very edge of the dispersion curve of one of the supermodes in the C-PCWs. In this regard, our original fast and accurate method is used to efficiently calculate the supermodes of the C-PCW system. The underlying semi-analytical full-wave modal analysis is based on the evaluation of the lattice sums for complex wavenumbers using the transition-matrix method in combination with the generalized reflection-matrix approach. As a proof of concept successful pulse operation of the all-optical AND logic gate is demonstrated in the framework of extensive full-wave finite-difference time-domain electromagnetics analysis.
We explore the discrete nature of waveguide modes and the effective medium concept to achieve an ultra-compact highly efficient mode conversion device in a high-index platform such as a silicon waveguide. The proposed...
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We explore the discrete nature of waveguide modes and the effective medium concept to achieve an ultra-compact highly efficient mode conversion device in a high-index platform such as a silicon waveguide. The proposed device is based on a co-directional coupler that has a periodic variation in its refractive index along the propagation direction. The transverse variation of the index profile is calculated based on the interference pattern between the modes of interest. We show that mode conversion can be realized with dielectric metasurfaces engraved in the silicon waveguide. We derive the equation for effective index and show proof-of-concept numerical results of the device performance. We obtain conversion efficiencies of 95.4% between the TE0-TE1 modes over 8.91 mu m interaction distance and 96.4% between the TE0-TE2 over 6.32 mu m. The resulting coupling coefficient changes as a function of the interaction distance in a sinusoidal manner, which is crucial for constructive energy transfer from one mode to another. Such mode coupling devices have the potential for application in dispersion compensations, wavelength division multiplexing systems, and sensing. (C) 2019 Optical Society of America
Ultrasound imaging transducers possess serious trade-off design in performances between the penetration depth and the imaging resolution, which loses detection accuracy of diseases in large and deep-depth organs. To e...
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Ultrasound imaging transducers possess serious trade-off design in performances between the penetration depth and the imaging resolution, which loses detection accuracy of diseases in large and deep-depth organs. To ease this problem, this study combines a piezoelectric transducer with the waveguide technique to realize invasive imaging. However, conventional configurations with waveguides suffer from low input energy or low energy transmission efficiency, thus leading to the proposal of the double-parabolic-reflector focusing and guiding mechanism to achieve high power transmission. In this letter, three different physical configurations of waveguides for ultrasound propagation are compared in terms of acoustic pressure, power, and propagation modes. The proposed mechanism with double parabolic reflectors enhances the acoustic pressure at the tip of the cylindrical waveguide to over 17 times compared to the conventional mechanism and increases the total power flow to around 213 times. Due to the superior performances in powerful ultrasound transmission, the proposal is expected to widen the applications in ultrasound imaging, ultrasound therapeutics, and ultrasound microscopy. Published under license by AIP Publishing.
作者：
Wang, YanchengHan, ChenyangMei, DeqingZhejiang Univ
Sch Mech Engn State Key Lab Fluid Power & Mechatron Syst Hangzhou 310027 Zhejiang Peoples R China Zhejiang Univ
Sch Mech Engn Key Lab Adv Mfg Technol Zhejiang Prov Hangzhou 310027 Zhejiang Peoples R China
Polymer-based substrate with region-selective microstructures are crucial for many biomedical applications. Here, we explored a novel method based on standing surface acoustic waves (SSAWs) for the fabrication of loca...
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Polymer-based substrate with region-selective microstructures are crucial for many biomedical applications. Here, we explored a novel method based on standing surface acoustic waves (SSAWs) for the fabrication of localized polymer-based microstructures via a predefined waveguide. When the SSAWs are excited, the generated acoustic pressure field can be controlled in a predetermined region of the fluid surface through controlling the size and shape of the waveguide geometry. On the basis of the capillary wave motion, the generated acoustic pressure field can excite microwavy patterned structures on the surface. Then with use of ultraviolet (UV) solidification, the polymer-based substrates with region-selective patterned microstructures can be successfully fabricated. Both finite element modeling and experimental studies demonstrated that the polymer substrate with different region-selective microstructures can be achieved by selecting the pairs of interdigital transducers (IDTs) and shapes of the predefined waveguides. The results showed that the proposed method is effective for fabricating polymer-based substrate with region-selective microstructures and may have potential in cell-laden chips for tissue engineering, cell-cell interactions, and other biomedical applications.
We use our vector Maxwell's nonlinear eigenmode solver to study the stationary solutions in 2D cross-section plasmonic slot waveguides with isotropic Kerr nonlinear codes and anisotropic Kerr nonlinear cores. Firs...
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We use our vector Maxwell's nonlinear eigenmode solver to study the stationary solutions in 2D cross-section plasmonic slot waveguides with isotropic Kerr nonlinear codes and anisotropic Kerr nonlinear cores. First, for the isotropic case, we demonstrate that, even in the low-power regime, iD studies may not provide accurate and meaningful results compared to 2D ones. Second, we study, including at high powers, the link between the nonlinear parameter gamma(nl) and the change of the nonlinear propagation constant Delta beta. Third, we demonstrate that our approach is also valid for anisotropic waveguides, and we show how to improve by, a factor of 2, the figure of merit of nonlinear plasmonic slot waveguides using realistic materials. (C) 2018 Optical Society of America
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