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Spatial waveguide mode separation for acoustic waves in a meta-slab composed of subunits with graded thicknesses
摘要： A meta-slab composed of subunits with graded thicknesses is proposed for spatially separating the zeroth- and first-order acoustic waveguide modes according to the generalized Snell’s law. The phase velocity for the first-order mode depends on the waveguide thickness, whereas that for the zeroth-order mode does not. This enables the required phase-shift gradients of the meta-slab to be obtained for spatially separating the two waveguide modes. To design the meta-slab, analytic solutions are derived for the transmission coefficients and phase shifts of the incident acoustic waves with the two modes propagating through the subunits. Numerical simulations with transient finite-element analyses are implemented to demonstrate the propagation of the two waveguide modes. Sinusoidal signal and tone-burst excitations are applied in the analyses. The latter case shows that the two waveguide modes can be successfully separated in space by the designed meta-slab.
关键词： phase velocity,finite-element analyses,acoustic waveguide modes,meta-slab,transmission coefficients,phase shifts,generalized Snell’s law
更新于2025-09-23 15:19:57
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Surface Polariton‐Like s‐Polarized Waveguide Modes in Switchable Dielectric Thin Films on Polar Crystals
摘要： Surface phonon polaritons (SPhPs) and surface plasmon polaritons (SPPs), evanescent modes supported by media with negative permittivity, are a fundamental building block of nanophotonics. These modes are unmatched in terms of field enhancement and spatial confinement, and dynamical all-optical control can be achieved, e.g., by employing phase-change materials. However, the excitation of surface polaritons in planar structures is intrinsically limited to p-polarization. On the contrary, waveguide modes in high-permittivity films can couple to both p- and s-polarized light, and in thin films, their confinement can become comparable to surface polaritons. Here, it is demonstrated that the s-polarized waveguide mode in a thin Ge3Sb2Te6 (GST) film features a similar dispersion, confinement, and electric field enhancement as the SPhP mode of the silicon carbide (SiC) substrate, while even expanding the allowed frequency range. Moreover, it is experimentally shown that switching the GST film grants nonvolatile control over the SPhP and the waveguide mode dispersions. An analytical model is provided for the description of the GST/SiC waveguide mode and it is shown that the concept is applicable to the broad variety of polar crystals throughout the infrared spectral range. As such, complementarily to the polarization-limited surface polaritons, the s-polarized waveguide mode constitutes a promising additional building block for nanophotonic applications.
关键词： waveguide modes,infrared spectral range,phase-change materials,surface plasmon polaritons,silicon carbide,nanophotonics,Ge3Sb2Te6,surface phonon polaritons,s-polarized light
更新于2025-09-19 17:13:59
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Giant tunable nonreciprocity of light in Weyl semimetals
摘要： The propagation of light in Weyl semimetal films is analyzed. The magnetic family of these materials is known by anomalous Hall effect, which, being enhanced by the large Berry curvature, allows one to create strong gyrotropic and nonreciprocity effects without external magnetic field. The existence of nonreciprocal waveguide electromagnetic modes in ferromagnetic Weyl semimetal films in the Voigt configuration is predicted. Thanks to the strong dielectric response caused by the gapless Weyl spectrum and the large Berry curvature, ferromagnetic Weyl semimetals combine the best waveguide properties of magnetic dielectrics or semiconductors with strong anomalous Hall effect in ferromagnets. The magnitude of the nonreciprocity depends both on the internal Weyl semimetal properties, the separation of Weyl nodes, and the external factor, the optical contrast between the media surrounding the film. By tuning the Fermi level in Weyl semimetals, one can vary the operation frequencies of the waveguide modes in THz and mid-IR ranges. Our findings pave the way to the design of compact, tunable, and effective nonreciprocal optical elements.
关键词： Weyl semimetals,optical elements,anomalous Hall effect,nonreciprocity,waveguide modes
更新于2025-09-11 14:15:04
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[Springer Series in Optical Sciences] Fano Resonances in Optics and Microwaves Volume 219 (Physics and Applications) || Multiple-Resonance Interference in Metallic Nanohole Arrays
摘要： In metallic nanohole arrays, the surface plasmon polaritons on the metal surfaces and the waveguide modes in the nanoholes are combined to form multipole surface plasmons. If these surface bound modes appear in a narrow frequency range, interference between multiple resonances and yields various resonant peak-dip structures in transmission, reflection and absorption spectra. In this chapter, we discuss the theoretical details of the mechanism of the multiple-resonance interference in metallic nanohole array systems using spatial and temporal coupled mode methods.
关键词： Fano resonance,surface plasmon polaritons,metallic nanohole arrays,waveguide modes,multiple-resonance interference,EIT-like phenomena
更新于2025-09-10 09:29:36