Actively tuning optical transmission through hybrid metasurfaces incorporated with multifunctional active media holds great promise for the next generation optical devices. In the terahertz (THz) range, they remain rare due to the lack of dynamic and multifunctional designs and materials. Here, a vanadium dioxide (VO2)‐based hybrid metasurface is proposed to present multifunctional control of THz waves via electrically triggering and ultrafast optical excitation. By minimizing the thermal mass of VO2 and optimizing the VO2 patterns within two side gaps of the asymmetric split‐ring resonators, a hybrid metasurface which can tune the THz wave with an absolute modulation depth up to 54% and a figure of merit as high as 138% is hereby presented. The hybrid metasurface achieves a switching time of 2.2 s under the electrically triggering and offers an ultrafast modulation within 30 ps under the femtosecond pulse excitation. More interestingly, owing to the intrinsic hysteresis behavior of VO2, the hybrid metasurface exhibits distinguishing multistate transmission amplitudes with a single electrical input. In short, this study paves the way for robust multifunctionality in electric‐controlled terahertz switching, photonic memory, and ultrafast terahertz optics.

No abstract

controlling, [3] metalens, [4] and so on. Among these metasurfaces, noble metals such as gold and silver are the most common candidates for electromagnetic resonance, such as split-ring resonators, [5,6] cut wire antennas, [7] and fishnet structures. [8] Nevertheless, the metallic structures suffer from not only intrinsic absorption losses that severely limit their efficiency, but also their permanent optical properties which are difficult to be tuned by external stimuli. A feasible way to solve these problems is to employ tunable metasurfaces consisting of active media. Many kinds of active metasurfaces have been reported, including graphene, [9][10][11] transparent conducting oxides, [12] as well as various semiconductors like Si, [13,14] InAs, [15] and GaAs. [16,17] With the rapid development of active metasurfaces, numerous studies have been focused on the modulation of terahertz (THz) waves. Considerable research efforts have been devoted to the dynamic tuning of THz waves using different stimuli, such as thermal heating, [18] electrical triggering, [19] and optical excitation. [20] While intensive amplitude, phase, and polarization control of the terahertz waves have been investigated by plenty of research, achieving ultrafast and efficient modulation remains an open challenge in the THz regime. Graphene has been widely used to form plasmonic metasurfaces, as it is capable of tuning THz waves by optical pumping and electrostatic gating. [21,22] Nonetheless, the electronic doping of graphene reduces the modulation speed, and the low absorption of light due to its monolayer feature limits the modulation depth. GaAs and Si have been demonstrated to control THz waves using all-optical-induced free carrier (FC) dynamics in the semiconductors, respectively. [16,23] But the delay of photoexcited FCs is relatively long (≈1 ns) in these intrinsic semiconductors, which is an essential limitation for ultrafast modulation. More recently, hybrid metasurfaces, by integrating an ultrathin layer of spin-coated solution-processed perovskite with metallic resonators, achieved ultrafast all-optical switching with a time constant of 500 ps. [24,25] However, the photoactivity of the solution-processed perovskite is weak as the differential transmission under femtosecond pulse excitation is only about 5%. A detailed analysis of the previous THz tunable metasurfaces can be found in Table S1 in the Supporting Information.As the backbone of modern technology, Si not only plays a dominant role in electronics, but also emerges as an excellent Metasurfaces have been widely used to manipulate terahertz waves due to their great potential for achieving unique electromagnetic responses. However, to realize ultrafast and efficient control of the light in active metasurfaces is still a critical challenge. Here, an ultrafast tunable metasurface which consists of ion-implanted and annealed silicon disk array is experimentally demonstrated in the terahertz range. By utilizing the optical-pump terahertz-probe spectroscopy, the absolute transmis...