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Dielectric metasurfaces have made great progress over the past decade to enhance light-matter interaction. Recently, dielectric nanohole structures have been employed for the creation of dielectric metasurfaces. However, the optical characteristics of most dielectric nanohole structures remain fixed once they are manufactured. This study investigates the optical properties of Ge2Sb2Te5 (GST) film perforated with a periodic dual nanohole array. The GST dual nanohole array is capable of supporting multiple guided resonances and bound states in the continuum (BICs). By introducing asymmetry in the radius, BICs can be transformed into quasi-BICs with high- Q resonances. The wavelengths of guided resonances and quasi-BICs can be dynamically controlled through the phase transition of GST. Furthermore, modifying the gap allows for the achievement of active high- Q electromagnetically induced transparency, resulting from the interaction between one guided resonance and one quasi-BIC mode. The GST asymmetric nanohole array holds potential for applications in optical modulators, slow-light devices, and nonlinear optical devices. [ABSTRACT FROM AUTHOR]

Dielectric metasurfaces have made significant advancements in the past decade for enhancing light–matter interaction at the nanoscale. Particularly, bound states in the continuum (BICs) based on dielectric metasurfaces have been employed to enhance nonlinear harmonic generation. However, conventional nonlinear metasurfaces are typically fixed in their operating wavelength after fabrication. In this work, we numerically demonstrate tunable third harmonic generation (THG) by integrating a dielectric metasurface with the phase-change material Ge2Sb2Te5 (GST). The hybrid phase-change metasurface can support two BICs with different electromagnetic origins, which are transformed into two high-Q quasi-BICs through the introduction of structural asymmetry. The two quasi-BICs are selectively excited by controlling the polarization of incident light, and their wavelengths are tunable due to the phase transition of GST. Notably, the efficiency of THG is significantly enhanced at the fundamental wavelengths corresponding to the two quasi-BICs, and the operating wavelength for THG enhancement can be dynamically tuned through the GST phase transition. Furthermore, the wavelength of THG enhancement can be further tuned by manipulating the polarization of pump light. Additionally, a high-Q analog of electromagnetically induced transparency is numerically achieved through the interaction between a low-Q Mie resonance and a quasi-BIC mode, which also improves the THG efficiency. The high-Q polarization-controlled hybrid phase-change metasurface holds promise for applications in dynamically tunable nonlinear optical devices. [ABSTRACT FROM AUTHOR]

Broadband tuning of polarization states is pivotal yet challenging in modern photonics technologies, especially for miniaturized or integrated systems. Metasurfaces potentially provide an effective approach to resolve this challenge. However, once a metadevice is fabricated, its functionalities are determined, and it is hard to actively tune the polarization states. Here, the electrically tunable broadband polarization states by combining phase‐change material (vanadium dioxide) and dispersion‐free metasurface are demonstrated for the first time. The polarization states are modulated through the electrically driven, Joule‐heat‐induced phase transition of vanadium dioxide, where the output polarization state can be continuously tuned from horizontal one to vertical one, or from circular polarization to linear polarization. With accurate on‐chip control of the phase transition, continuous and reversible modulation of polarization is verified in a scanning display. Moreover, a proof‐of‐concept demonstration for dynamically independent control of multiple polarization display is carried out. Different images are produced by applying electrical currents in N separate channels to generate a dynamic multiplexing polarization display with 2N encoding states. Such an active metasurface can be readily integrated with electronics and has potential applications in display, encryption, camouflage, and information processing. [ABSTRACT FROM AUTHOR]