A key recent advance in nanophotonics field has been the emergence of tunable, switchable and reconfigurable metasurfaces offering “optical properties on demand”. With these devices, light propagation does not have to be static, as traditionally assumed, but may be changed at will at any point in space and/or moment in time. Various approaches have been developed to realize optical components made from metadevices reconfigurable by mechanical, electrical, or optical means. In general, however, most of the existing reconfigurable metasurfaces tune the properties over the entire device homogeneously when stimulated. The ability to tailor the optical properties of individual meta-molecules in planar metasurfaces promises to open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping and adaptive optics. In this work, we pioneered the novel single-meta-molecule addressable digitally reconfigurable metadevices using the emerging paradigms of tunable metasurfaces - functional matter structured on the sub-wavelength scale, and by engaging new ideas of phase-change material integrated with nanostructures for dynamic light control. In our design, low loss dielectric nanostructures (amorphous Si nanorods) are patterned on top of phase-change foundation structures to form the hybrid meta-molecule. As for the phase-change medium, we use the chalcogenide glasses (e.g. germanium-antimony-telluride), which is widely exploited in rewritable optical disk storage technology and non-volatile electronic memories due to its good thermal stability, high switching speed, large number of achievable rewriting cycles and pronounced contrast of dielectric properties observed between two phases. The phase-change process in chalcogenide glasses is a material reaction to the photothermal effects. Using tightly-focused low-energy fs laser pulses to excite the phase transition results in a sharp border between the amorphous background and crystallized spots, allowing individual single meta-molecules to be addressed. The reconfiguration of meta-molecules will be accomplished by re-amorphization of the phase-change material with a high-energy single optical pulse. The preliminary simulation results demonstrated the reconfigurable metasurfaces for phase and resonance frequency modulation of light based on the innovative platform of digitally and individually reconfigurable meta-molecules for applications in active beam shape and hologram display. This development will progress photonic technology enabling increased information flow, while reducing power consumption and achieving new levels of miniaturization for photonic devices.
Qian Wang, Shengtao Mei, Guanghui Yuan, Kian Shen Kiang, Nikolay I. Zheludev, and Jinghua Teng, "Digitally tunable metasurfaces based on phase-change material (Conference Presentation)," Proc. SPIE 10671, Metamaterials XI, 106711J (Presented at SPIE Photonics Europe: April 25, 2018; Published: 23 May 2018); https://doi.org/10.1117/12.2309888.5788797212001.
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