In this paper, we present a thorough investigation for a spontaneous parametric four-wave mixing process in third-order nonlinear waveguides with various continuous tapering patterns. It has been previously shown that...
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In this paper, we present a thorough investigation for a spontaneous parametric four-wave mixing process in third-order nonlinear waveguides with various continuous tapering patterns. It has been previously shown that these devices can quasi-phase-match the four-wave mixing process and enhance its conversion efficiency by orders of magnitude. By altering the tapering profile curve we found that these devices can enable single-photon sources with either narrow or broadband spectral widths at on-demand frequencies. Using our model, we were also able to identify the waveguide length at which the single-photon spectral purity is maximized.
In this work, we investigate the nonperturbative decay dynamics of a quantum emitter coupled to a composite right-/left-handed transmission line. Our theory captures the contributions from the different spectral featu...
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In this work, we investigate the nonperturbative decay dynamics of a quantum emitter coupled to a composite right-/left-handed transmission line. Our theory captures the contributions from the different spectral features of the waveguide, providing an accurate prediction beyond the weak coupling regime and illustrating the multiple possibilities offered by the nontrivial dispersion of metamaterial waveguides. We show that the waveguide is characterized by a bandgap with two asymmetric edges: (i) a mu-near-zero band edge, where spontaneous emission is inhibited and an unstable pole is smoothly transformed into a bound state, and (ii) an epsilon-near-zero band edge, where the decay rate diverges and unstable and real (bound state) poles coexist. In both cases, branch cut singularities contribute with fractional decay dynamics whose nature depends on the properties of the band edges.
On-chip mid-infrared (MIR) supercontinuum generation (SCG) covering the molecular functional spectral region (3-12 mu m) offers the advantages of robustness, simplicity, and compactness. Yet, the spectral range still ...
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On-chip mid-infrared (MIR) supercontinuum generation (SCG) covering the molecular functional spectral region (3-12 mu m) offers the advantages of robustness, simplicity, and compactness. Yet, the spectral range still cannot be expanded beyond 10 mu m. In this study, on-chip ultrabroadband MIR SCG in a high numerical aperture chalcogenide (ChG) waveguide is numerically investigated. The ChG waveguide with a Ge-As-Se-Te core and Ge-Se upper and lower cladding is designed to optimize the nonlinear coefficients and dispersion profile. Assisted by dispersive wave generation in both short- and long-wavelength range, broadband SCG ranging from 2 to 13 mu m is achieved. Besides, a fabrication scheme is proposed to realize precise manipulation of dispersion design. Such results demonstrate that such sources are suitable for compact, chip-integrated molecular spectroscopy applications.
Glide symmetry offers new degrees of freedom to engineer the properties of periodic structures, and thus it has been exploited in various electromagnetic structures. However, so far there has been little exploration o...
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Glide symmetry offers new degrees of freedom to engineer the properties of periodic structures, and thus it has been exploited in various electromagnetic structures. However, so far there has been little exploration on the impact that glide symmetry can offer in the field of acoustics. In this paper, we explore glide-symmetric acoustic waveguides, highlighting their dispersion characteristics and guiding properties and demonstrating opportunities in the context of acoustic devices. Here we analytically derive their dispersive features applying a semianalytical mode-matching technique. We then demonstrate how the unusual dispersion properties of glide-symmetric acoustic waveguides can be used to achieve very sharp frequency responses. Based on these results, we propose a sensing platform for liquid analytes that exhibits large sensitivity and linearity. Furthermore, by introducing fluid motion, we leverage these responses to design an acoustic isolator based on acoustic Mach-Zehnder interferometry, whose design is more favorable in terms of footprint and complexity in comparison to other acoustic nonreciprocal devices that do not rely on glide symmetry.
We study transport properties and the formation of bound states in the continuum (BIC) in asymmetric quantum mechanical and electromagnetic waveguides. An analytical model for an arbitrary asymmetric two-terminal quan...
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We study transport properties and the formation of bound states in the continuum (BIC) in asymmetric quantum mechanical and electromagnetic waveguides. An analytical model for an arbitrary asymmetric two-terminal quantum mechanical waveguide is proposed, and conditions of BIC formation are formulated. We show that the Friedrich-Wintgen mechanism of BIC formation in a system coupled to two continua takes place regardless of the symmetry of the system as long as the proportionate coupling condition is fulfilled. This result is illustrated by numerical simulation of two-dimensional quantum billiard and optical waveguide with a cavity. Due to the universal wave nature of BIC, the proposed BIC formation mechanism allows one to obtain BICs in the broader class of quantum mechanical, electromagnetic, acoustic, and other types of structures.
Photonic topological edge states are robust against the structural disorder, paving the way of their broad applications in the field of photonics. In the meantime, the topological phase transitions of parity-time (PT)...
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Photonic topological edge states are robust against the structural disorder, paving the way of their broad applications in the field of photonics. In the meantime, the topological phase transitions of parity-time (PT) symmetric systems have been extensively investigated. This report presents another new concept, PT symmetric photonic topological waveguides, being PT symmetric as a whole, but with gain/loss waveguides supporting topological edge modes. Through the theoretical and numerical investigations, we demonstrate unidirectional propagation in valley-Hall photonic topological coupled waveguides in a PT-broken phase as an example. Such waveguides can exhibit numerous photonic functionalities observable in PT symmetric photonic systems, the performances of which are robust against the defects due to the topological nature of the constituent waveguides.
Controlling the low-energy excitations in magnetically active materials is the key to numerous phenomena in magnonics and spintronics. This study demonstrates a generic scheme for highly efficient control of magnonic ...
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Controlling the low-energy excitations in magnetically active materials is the key to numerous phenomena in magnonics and spintronics. This study demonstrates a generic scheme for highly efficient control of magnonic signals in a stack of magnetic slabs separated by current-carrying metallic nanoscale spacer layers. We demonstrate analytically and confirm full numerically that the proposed structure has a magnonic spectrum that is highly susceptible to external perturbations and is governed by a parity-time (PT) symmetric Hamiltonian. The enhanced sensitivity can be tuned by the dc charge currents, the number of stacking layers or/and by the intrinsic properties of the stacking layers. Physically, the currents in the spacer layers cause spin-orbit torques acting on the adjacent magnetic layers. Effectively, these torques damp or antidamp magnonic excitations. Depending on the spacer-charge current density and the number of stacking layers, a point can be reached where damping and antidamping are balanced. Beyond this exceptional point (EP) the magnonic system enters a PT-symmetry-broken phase. Near EP we show analytically and numerically that the system exhibits a nonlinear response even to weak perturbing fields. Scanning the external fields in a loop to enclose the EP in the dispersion manifold, we identify a nonreciprocal topological energy transfer between different magnon modes. The results point to a promising route in magnonics and spintronics as well as to a versatile testing ground for PT-symmetry-driven phenomena.
The AlGaAs material platform has been intensively used to develop nonlinear photonic devices on-a-chip, thanks to its superior nonlinear optical properties. We propose a new AlGaAs waveguide geometry, called half-core...
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The AlGaAs material platform has been intensively used to develop nonlinear photonic devices on-a-chip, thanks to its superior nonlinear optical properties. We propose a new AlGaAs waveguide geometry, called half-core etched, which represents a compromise between two previously studied geometries, namely the nanowire and strip-loaded waveguides, combining their best qualities. We performed tunable four-wave mixing (FWM) experiments in all three of these geometries in the telecommunications C-band (wavelengths around 1550 nm), with a pulsed pump beam and a continuous-wave (CW) signal beam. The maximum FWM peak efficiencies achieved in the nanowire, strip-loaded and half-core geometries were about -5 dB, -8 dB and -9 dB, respectively. These values are among the highest reported in AlGaAs waveguides. The signal-to-idler conversion ranges were also remarkable: 161 nm for the strip-loaded and half-core waveguides and 152 nm for the nanowire. Based on our findings, we conclude that the half-core geometry is an alternative approach to the nanowire geometry, which has been earlier deemed the most efficient geometry, to perform wavelength conversion in the spectral region above the half-bandgap. Moreover, we show that the half-core geometry exhibits fewer issues associated with multiphoton absorption than the nanowire geometry.
This article explains the propagation of flexural waves of membrane acoustic metamaterials and waveguide effects from the perspective of modal analysis. The flexural band gaps are calculated with both single and doubl...
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This article explains the propagation of flexural waves of membrane acoustic metamaterials and waveguide effects from the perspective of modal analysis. The flexural band gaps are calculated with both single and double periodic Bloch-Floquet boundary conditions. The unit cells with one and two masses attached to the membrane are applied to get the transmittance of the flexural wave on a beam/plate. Local resonance and Bragg scattering mechanism is analyzed in detail through mode cloud image. The topological waveguide plates are designed based on structural asymmetry. The proposed MAM waveguide is strongly related to the rotation angle of the attached dual-mass. Finally, the dispersion relation of the supercell indicates the energy dissipation mechanism in the waveguide path. (C) 2021 Elsevier B.V. All rights reserved.
Integrated optical waveguides have been widely explored in the context of quantum simulation for various physical models based on paraxial diffraction of light, which are described by an equivalent Schrödinger eq...
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Integrated optical waveguides have been widely explored in the context of quantum simulation for various physical models based on paraxial diffraction of light, which are described by an equivalent Schrödinger equation. The physics in these systems can be formulated using the tight-binding models, in which the coupling between the waveguides can be tuned independently in a wide range, providing an excellent platform for simulation of various phenomena. In this work, we build a tight-binding model with parameters transported directly from two coupled waveguides, which are controlled by dielectric constant change, site distance, and geometries. This design principle can greatly save the simulation and experimental cost in real implementation. As compared with results from the exact simulation based on Maxwell equations, our numerical results demonstrate that the physics of the one- or two-dimensional large lattice systems could be well described by our tight-binding model, exhibiting the excellent transferability of the parameters in two coupled waveguides. In addition, some applications are further discussed: we show how to realize the topological Su-Schrieffer-Heeger (SSH) model, kinked SSH model, and study their associated topological phases and edge modes. Some two-dimensional models based on our tight-binding models are also discussed. Lastly, more intriguing applications, such as nonlinearity or disorder-induced effect and generation of the gauge potential are also briefly discussed. Our work intuitively provides an effective reference route for designing models for experiments and demonstrates the practicality of using the tight-binding approximation to solve complicated models. The design principle demonstrated in this work paves the foundation for the application of optical waveguides based on more complicated models, and will be readily verified experimentally in the near future.
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