• Current Optics and Photonics
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• v.7 no.3
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• pp.254-262
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• 2023

Novel thermo-optically focus-switchable Fresnel zone plates based on phase-change metafilms are designed and analyzed at a visible wavelength (660 nm). By virtue of the large thermo-optic response of vanadium dioxide (VO₂) thin film, a phase-change material, four different plasmonic phase-change absorbers are numerically designed as actively tunable Gires-Tournois Al-VO₂ metafilms in two and three dimensions. The designed phase-change metafilm unit cells are used as the building blocks of actively focus-switchable Fresnel zone plates with strong focus switching contrast (40%, 83%) and high numerical apertures (1.52, 1.70). The Fresnel zone plates designed in two and three dimensions work as cylindrical and spherical lenses in reflection type, respectively. The coupling between the thermo-optic effect of VO₂ and localized plasmonic resonances in the Al nanostructures offer a large degree of freedom in design and high-contrast focus-switching performance based on largely tunable absorption resonances. The proposed method may have great potential in photothermal and electrothermal active optical devices for nonlinear optics, microscopy, 3D scanning, optical trapping, and holographic displays over a wide spectral range including the visible and infrared regimes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.9
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• pp.685-692
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• 2018

Using Babinet's principle and generalized sheet transition conditions(GSTCs), an analysis method for metascreens is proposed. First, the relation of a complementary screen between a metafilm and metascreen with the same dimensions was confirmed using Babinet's principle. These properties were verified by comparing the reflection coefficient of the patch and the transmission coefficient of the mesh. The patch and mesh are the basic structures of metafilms and metascreens, respectively. Based on these findings, it is also confirmed that the reflection coefficient of the patch surface calculated by GSTCs has the same value as the transmission coefficient of the mesh surface. It is expected that the proposed analysis methods can be applied to the magnitude, phase, and polarization of electromagnetic waves in the various unit structures of a given metasurface.