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| Structure chart of ultrafast all-optical terahertz modulation. (a) Schematic illustration of hybrid structure combining Ge film with inverse-designed metasurface at the pump light of 800 nm for terahertz modulation. (b) Processed inverse-designed metasurface structure without Ge film covering on the face. (c) Processed inverse-designed metasurface structure covering 200 nm thick Ge film on the face. The scale bar in the pictures is 50 μm. |
https://www.osapublishing.org/prj/fulltext.cfm?uri=prj-9-6-1099&id=451405
Metasurface plays a key role in various terahertz metadevices, while the designed terahertz metasurface still lacks flexibility and variety. On the other hand, inverse design has drawn plenty of attention due to its flexibility and robustness in the application of photonics. This provides an excellent opportunity for metasurface design as well as the development of multifunctional, high-performance terahertz devices. In this work, we demonstrate that, for the first time, a terahertz metasurface supported by the electromagnetically induced transparency (EIT) effect can be constructed by inverse design, which combines the particle swarm optimization algorithm with the finite-difference time-domain method. Incorporating germanium (Ge) film with inverse-designed metasurface, an ultrafast EIT modulation on the picosecond scale has been experimentally verified. The experimental results suggest a feasibility to build the terahertz EIT effect in the metasurface through an optimization algorithm of inverse design. Furthermore, this method can be further utilized to design multifunctional and high-performance terahertz devices, which is hard to accomplish in a traditional metamaterial structure. In a word, our method not only provides a novel way to design an ultrafast all-optical terahertz modulator based on artificial metamaterials but also shows the potential applications of inverse design on the terahertz devices.
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