Bi₂Se₃-Functionalized Metasurfaces for Ultrafast All-Optical Switching and Efficient Modulation of Terahertz Waves

Abstract

Because of the wealth of fascinating physical phenomena observed in topological insulators (TIs), their exciting properties have been intensively investigated for electronic and optoelectronic applications, such as quantum devices, saturable absorbers, and photodetectors, in the visible to terahertz (THz) spectral range. However, their potential for metaphotonic devices has yet to be explored. Here, we present a comprehensive investigation on the active photonic performance of a novel metaphotonic device by hybridizing ultrathin Bi2Se3 bridges into metamaterials in the THz range. Unlike THz modulation via Fano-like plasmon-phonon destructive interference in the pure Bi2Se3 structure, our Bi2Se3 microribbon arrays with high photoconductivity can short-circuit the circulating surface currents in the proposed metasurfaces, leading to remarkable electromagnetically induced transparency (EIT) transmission and group delay modulations at the operational frequency. Additionally, the width of the Bi2Se3 bridges is optimized to 20 μm to maximize the modulation depth, with the modulation of the transmission resonance amplitude and the group delay as high as 31% and 2.7 ps, respectively. Due to the short photocarrier lifetime in Bi2Se3 films (within a few picoseconds), the full recovery time after photoinjection is less than 9.5 ps, enabling an ultrafast switching speed up to a hundred GHz. The ultrafast and effective control of the light spectrum in Bi2Se3-functionalized metaphotonic systems lays the foundation for promoting the emergence of TI-based optoelectronics.