Highly Confined and Switchable Mid-Infrared Surface Phonon Polariton Resonances of Planar Circular Cavities with a Phase Change Material

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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.

Section: Methodsmentioning

confidence: 99%

Surface Polariton‐Like s‐Polarized Waveguide Modes in Switchable Dielectric Thin Films on Polar Crystals

Paßler

Heßler

Wuttig

et al. 2019

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Section: Phonon Polaritons In Low‐dimensional Materialsmentioning

confidence: 99%

“…The dynamic control is unambiguously revealed in the nano‐FTIR around the two reststrahlen bands of hBN (Figure f): the in‐plane and out‐of‐the plane phonon resonances are dynamically tuned by controlling the temperature of the hBN/VO 2 vdW heterostructure. Note that in addition to VO 2 , the phonon polaritons can be tuned with other phase change materials, for example Ge 3 Sb 2 Te 6 (GST) where the dispersion of phonon polaritons were altered with photoinduced phase transition (Figure g): the erasing of the polariton dipolar modes were observed via the transition from amorphous‐GST (top) to crystalline‐GST (bottom).…”

Section: Phonon Polaritons In Low‐dimensional Materialsmentioning

confidence: 99%

Phonon Polaritons and Hyperbolic Response in van der Waals Materials

Shen

Qiu

et al. 2019

113

Phonon polaritons provide useful opportunities, complementary to those provided by plasmon polaritons, in the study of the interaction of light with matter at small scales. The focus of this review is on phonon polaritons in low‐dimensional van der Waals (vdW) materials and heterostructures. Phonon polaritons confined in vdW materials exhibit large electromagnetic localization and are easy to hybridize with other collective modes. The extreme optical anisotropy in vdW systems produces the natural hyperbolic dispersion, enabling the access to deep subdiffractional optics and often yielding improved figures of merit over hyperbolic metamaterials. These virtues hold promises for practical nanophotonic applications, including optical sensing, super‐resolution imaging, energy and emission engineering, quantum optics, and a next generation of optical circuit elements.

“…A different approach involves the excitation and tuning of phonon polaritons in quartz, silicon carbide (SiC), or hexagonal boron nitride (hBN), which feature very low losses. [ 23,32,33 ]…”

Section: Figurementioning

confidence: 99%

The Potential of Combining Thermal Scanning Probes and Phase‐Change Materials for Tunable Metasurfaces

Michel

Meyer

Essing

et al. 2020

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ultra-thin equivalents, but may also introduce new functionalities (phase discontinuities, anomalous reflection, and refraction, etc.). [2,3] However, the shape of the wavefront is defined by the metasurface design, including material selection and geometry, and is fixed after fabrication. Active postfabrication control requires the tunability of the optical response of each metasurface element. [4,5] One common approach for active metasurfaces is to capitalize on the change of the material polarizabilityeither of the scatterer or its surroundings. This can be achieved, for example, by modulation of the charge density in doped semiconductors (e.g., GaAs) or graphene, [6] by changing the state of liquid crystals adjacent to metallic antennas, [7] or by including phase-transition (e.g., vanadium dioxide VO 2) [8-10] or phase-change [e.g., germanium antimony telluride (GeTe) x (Sb 2 Te 3) 1−x ] [11] materials in the metasurface. Mechanical tuning with stretchable substrates or actuators, [12] chemical reactions at the scatterers, [13] or enhanced optical nonlinearities [14] are other possible approaches for post-fabrication tunability. Phase-change materials (PCMs) are among the best-suited materials to provide tunability of metasurfaces due to the property contrast between their amorphous (A) and crystalline (C) phase. [15] In contrast to phase-transition materials (e.g., VO 2), PCMs feature non-volatile states and thus, no energy is needed to maintain the material properties. The structural change is accompanied with a refractive index change Δn = |n C − n A | Metasurfaces allow for the spatiotemporal variation of amplitude, phase, and polarization of optical wavefronts. Implementation of active tunability of metasurfaces promises compact flat optics capable of reconfigurable wavefront shaping. Phase-change materials (PCMs) are a prominent material class enabling reconfigurable metasurfaces due to their large refractive index change upon structural transition. However, commonly employed laser-induced switching of PCMs limits the achievable feature sizes and restricts device miniaturization. Thermal scanning-probe-induced local switching of the PCM germanium telluride is proposed to realize near-infrared metasurfaces with feature sizes far below what is achievable with diffraction-limited optical switching. The design is based on a planar multilayer and does not require fabrication of protruding resonators as commonly applied in the literature. Instead, it is numerically demonstrated that a broad-band tuning of perfect absorption can be realized by the localized tip-induced crystallization of the PCM. The spectral response of the metasurface is explained using resonance mode analysis and numerical simulations. To facilitate experimental realization, a theoretical description of the tip-induced crystallization employing multiphysics simulations is provided to demonstrate the great potential for fabricating compact reconfigurable metasurfaces. The concept can be applied not only for plasmonic sensing and spatial freq...