Terahertz (THz) modulators are crucial components in terahertz high-speed communications and interconnections. In this article, we demonstrate a high-efficiency broadband terahertz graphene composite modulator. The mo...
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Terahertz (THz) modulators are crucial components in terahertz high-speed communications and interconnections. In this article, we demonstrate a high-efficiency broadband terahertz graphene composite modulator. The modulator is composed of a double-layer graphene integrated Si slot waveguide on a SiO2 substrate, which significantly enhances in-plane polarization matching and interaction between graphene and the THz wave. The transmission characteristics of the guided THz wave can be flexibly tuned by controlling the chemical potential of graphene. The modulator achieves excellent amplitude modulation performance, with a modulation depth of 99%, insertion loss of 0.0051 dB/mu m, modulation length of 300 mu m, modulation bandwidth of 19.59 GHz, and energy consumption of 384.5 pJ/bit at 1 THz. This work offers a potential solution for designing high-performance graphene-based THz modulators, with promising applications in future high-speed THz telecommunication and interconnect systems.
We investigate the quasi-coherent radiation from a train of electron bunches moving along the axis of a cylindrical waveguide, assuming that a part of the waveguide is filled with a dielectric medium. For the permitti...
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We investigate the quasi-coherent radiation from a train of electron bunches moving along the axis of a cylindrical waveguide, assuming that a part of the waveguide is filled with a dielectric medium. For the permittivity of the latter, the general case of dispersion is considered. It is shown that under certain conditions on the permittivity of the medium and on the values of the problem parameters, the waveguide modes become equidistant. As a consequence, quasi-coherent Cherenkov radiation from the train of bunches may be generated on the first several waveguide modes simultaneously. An example of dispersion law is provided for which the corresponding Cherenkov radiation is suppressed.
Thermoacoustic waveguides are systems of hollow tubes and thermally graded porous segments that can operate as active materials where acoustic waves receive energy from an external heat source. This work demonstrates ...
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Thermoacoustic waveguides are systems of hollow tubes and thermally graded porous segments that can operate as active materials where acoustic waves receive energy from an external heat source. This work demonstrates that by adjusting the pore geometry several unique low-frequency propagation features arise from the complex-valued band structure of periodic thermoacoustic waveguides that reflect into the acoustic pressure field within finite-length systems. Numerical methods have been employed to model waveguides with porous segments constituted by cylindrical inclusions (parallel pins). In periodic structures, a critical frequency emerges where the sign of the refractive index in one direction of propagation changes, thus zero- and negative-unidirectional refractive index, unidirectional energy transport, and amplification/attenuation crossover effects may take place. On the other hand, the study of the acoustic pressure field shows that, for wave packets with either direction of propagation, finite-length waveguides may behave as active acoustic metamaterials with zero- or negative-refractive index. The acoustic pressure field in the waveguide, generated by an upstream source, may exhibit increasing amplitude and phase recovery farther away from the source, mimicking the field created by a downstream source, propagating upstream in a non-active medium.
We investigate the formation of multipole topological solitons at the edges of two and three coupled parallel Su-Schrieffer-Heeger (SSH) waveguide arrays. We show that independent variations of waveguide spacing in th...
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We investigate the formation of multipole topological solitons at the edges of two and three coupled parallel Su-Schrieffer-Heeger (SSH) waveguide arrays. We show that independent variations of waveguide spacing in the unit cells (dimers) in coupled waveguide arrays result in the emergence at their edges of several topological edge states with different internal symmetries. The number of emerging edge states is determined by how many arrays are in topologically nontrivial phase. In the presence of nonlinearity, such edge states give rise to families of multipole topological edge solitons with distinct stability properties. Our results illustrate that coupling between quasi-onedimensional topological structures substantially enriches the variety of stable topological edge solitons existing in them. (c) 2024 Optica Publishing Group. All rights, including for text and data nologies, are reserved.
A metal-loaded graphene surface plasmon waveguide composed of a thin silica layer sandwiched between a graphene layer and a metal stripe is proposed and the waveguiding properties in the THz regime are numerically inv...
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A metal-loaded graphene surface plasmon waveguide composed of a thin silica layer sandwiched between a graphene layer and a metal stripe is proposed and the waveguiding properties in the THz regime are numerically investigated. The results show that the fundamental mode of the proposed waveguide is tightly confined in the middle silica layer with an acceptable propagation loss. Compared with most other graphene waveguides proposed in the literature, the realization of this waveguide does not need to pattern or deform the graphene layer, thus retaining the superior properties of bulk graphene material. The tight modal confinement and the ease of fabrication suggest the high potential use of this waveguide in high-density THz photonic integration. (C) 2015 Elsevier B.V. All rights reserved.
The waveguide acoustic black hole (WAB) effect is a promising approach for controlling wave propagation in various applications, especially for attenuating sound waves. While the wave-focusing effect of structural aco...
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The waveguide acoustic black hole (WAB) effect is a promising approach for controlling wave propagation in various applications, especially for attenuating sound waves. While the wave-focusing effect of structural acoustic black holes has found widespread applications, the classical ribbed design of waveguide acoustic black holes (WABs) acts more as a resonance absorber than a true wave-focusing device. In this study, we employ a computational design optimization approach to achieve a conceptual design of a WAB with enhanced wave-focusing properties. We investigate the influence of viscothermal boundary losses on the optimization process by formulating two distinct cases: one neglecting viscothermal losses and the other incorporating these losses using a recently developed material distribution topology optimization technique. We compare the performance of optimized designs in these two cases with that of the classical ribbed design. Simulations using linearized compressible Navier-Stokes equations are conducted to evaluate the wave-focusing performance of these different designs. The results reveal that considering viscothermal losses in the design optimization process leads to superior wave-focusing capabilities, highlighting the significance of incorporating these losses in the design approach. This study contributes to the advancement of WAB design and opens up new possibilities for its applications in various fields.
Photonic platforms invariant under parity (P), time-reversal (T), and duality (D) can support topological phases analogous to those found in time-reversal invariant Z2 electronic systems with conserved spin. Here, we ...
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Photonic platforms invariant under parity (P), time-reversal (T), and duality (D) can support topological phases analogous to those found in time-reversal invariant Z2 electronic systems with conserved spin. Here, we demonstrate the resilience of the underlying spin Chern phases against non-Hermitian effects, notably material dissipation. We identify that non-Hermitian, PD-symmetric, and reciprocal photonic insulators fall into two topologically distinct classes. Our analysis focuses on the topology of a PD-symmetric and reciprocal parallel-plate waveguide (PPW). We discover a critical loss level in the plates that marks a topological phase transition. The Hamiltonian of the PTD-symmetric system is found to consist of an infinite direct sum of Kane-Mele-type Hamiltonians with a common band gap. This structure leads to the topological charge of the waveguide being an ill-defined sum of integers due to the particle-hole symmetry. Each component of this series corresponds to a spin-polarized edge state. Our findings present a unique instance of a topological photonic system that can host an infinite number of edge states in its band gap.
The spatial resolution of near-field magnetic probes is a crucial performance metric for conducting spatial field measurements in practical applications. However, the commonly adopted approaches for determining the sp...
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The spatial resolution of near-field magnetic probes is a crucial performance metric for conducting spatial field measurements in practical applications. However, the commonly adopted approaches for determining the spatial resolution of the probe face substantial ambiguity and limitations. Addressing this issue, a generalized definition of magnetic probe spatial resolution is proposed, which correlates directly with the effective size of the probe's sensing front end. Following this definition, a novel calibration method is introduced, utilizing the evanescent field within a rectangular waveguide structure. This calibration method is implemented on the basis of a custom-designed transverse electromagnetic (TEM) cell, whose performance has been validated both in simulations and in experiments. The proposed method effectively mitigates uncertainties arising from the measurement position and field distribution, enabling a universal and accurate assessment of the spatial resolution of the probe. The efficacy of the calibration method is validated on a commercial magnetic probe. The comparative analysis demonstrates that the proposed calibration technique yields significantly improved accuracy compared to the existing method for determining the spatial resolution of the probe.
We demonstrate an on-chip photodetector by integrating a graphene and topological insulator Bi2Te3 heterostructure on a thin-film lithium niobate waveguide. Lithium niobate on insulator (LNOI) waveguides are fabricate...
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We demonstrate an on-chip photodetector by integrating a graphene and topological insulator Bi2Te3 heterostructure on a thin-film lithium niobate waveguide. Lithium niobate on insulator (LNOI) waveguides are fabricated by the photolithography-assisted chemical mechanical etching method. The bismuth telluride (Bi2Te3) and graphene heterostructure design provides enhanced photocurrent due to the effective photocarrier generation. The lithium niobate waveguide-integrated Bi2Te3/graphene heterojunction presents a high absorption coefficient of 2.1 dB/mu m. The Bi2Te3/graphene heterojunction photodetector exhibits a responsivity of 2.54 mA/W without external bias at a 1.55 mu m wavelength, which is enhancement of sevenfold as compared to the pure graphene-based photodetector. The photodetector has a 3 dB bandwidth of over 4.7 GHz. This work provides a potentially viable method for a self-powered, high responsivity, and fast response of the photodetector integrated with the LNOI photonic platform. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.
In this paper, a marching solver designed for the computation of wave propagation is developed within a class of open three-dimensional waveguides. For the wave propagation model, a three-dimensional scalar and freque...
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In this paper, a marching solver designed for the computation of wave propagation is developed within a class of open three-dimensional waveguides. For the wave propagation model, a three-dimensional scalar and frequency-domain Helmholtz equation is effectively adopted. Specifically, the boundary value problem is converted into an initial value problem by the Dirichlet-to-Neumann (DtN) mapping. Then, with the solving domain restricted to a class of cuboid waveguides, a numerical marching method based on DtN mapping is well established. Besides, when a class of open waveguides is included in the solving domain, the perfectly matched layer (PML) can be used to change the open domain into the bounded form (cuboid waveguide). Finally, the original Helmholtz equation now is equivalent to a complex differential equation with the second order, whose corresponding numerical marching method is also triggered. Numerical comparisons show that the marching method based on the DtN mapping is more efficient and feasible than the one-way method (that is, the beam propagation method (BPM)) when solving the three-dimensional Helmholtz equation. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
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