## 4 Active Switching of Fano Resonances  
To excite the strong Fano resonance effect, we set the offset length to 16 \(\upmu\)m, and then obtain the MM structure with large asymmetry ratio. Figure 3a describes the transmission response of the proposed VO\({}_{2}\)-implanted MM structure for heating process. The blue curve represents the transmission spectrum of the metadevice at low temperature (45 \({}^{\circ}\)C). We only observe a broad eigen resonance mode at 0.700 THz excited by dipole resonance (acts as a bright mode), which has a wide bandwidth of 0.385 THz and low Q-factor of 3. When the VO\({}_{2}\)-implanted MM is radiated by thermal pump of 58 \({}^{\circ}\)C, the double Fano resonance modes are excited on both sides of the eigen resonance, including Fano 1 at 0.515 THz and Fano 2 at 1.160 THz (behaves as a dark mode). Upon further enhancement of the pumping heat, Fano resonance dips attenuates gradually, and a small red shift occurs at the resonance frequency, it is completely switched when the pump power is increased to 68 \({}^{\circ}\)C. The pumping temperature of 70 \({}^{\circ}\)C will not affect the Fano resonance any more. The observed Fano resonance in the thermally excited VO\({}_{2}\)-implanted MMs is mainly due to the destructive interference caused by the asymmetry of the structure. Its physical mechanism is the resonance interaction between the wide dipole mode and the sharp discrete mode. In order to characterize the resonance and tunable performance of the proposed metadevice, we calculated the Q-factor and modulation depth of the excited Fano resonances. It is exciting that although the calculated Q-factor of Fano 1 is only 5, but its modulation depth is as high as 99%. More importantly, compared with the intrinsic resonance mode, the resonance response of Fano 2 is obviously improved, the Q-factor is 33, which is much higher than that of the known MMs, simultaneously, and the modulation depth can reach 83%. This kind of MM with large modulation depth and high Q-factor has great potential in ultra-sensitive sensing and ultra-narrow band filtering applications. The excited strong Fano resonance can be completely switched-off by cooling the metadevice, but this process is not reversible. The simulation results in Figure 3b presents that when the external excitation temperature decreases from 70 \({}^{\circ}\)C to 64 \({}^{\circ}\)C, the strength of the observed Fano resonance has not been significantly weakened. Upon further reducing the pump power, Fano dips in the transmission spectrum abates gradually and it completely disappears when temperature drops to 45 \({}^{\circ}\)C. Therefore, compared with the thermal excitation process, it is difficult to switch off the Fano resonance using the cooling power. The simulation results shown in Figure 3 have clearly characterized the excellent switching performance of the metadevice. To describe the continuously tunable process more vividly under the  
Figure 3: Simulated THz transmission spectra of the proposed VO\({}_{2}\)-implanted MM structure corresponding to different temperatures, showing the active modulation of the two Fano resonances at 0.515 THz (Fano 1) and 1.160 THz (Fano 2): (**a**) heating process; (**b**) cooling process. external thermal excitation, the two-dimensional THz transmission spectrum changing with frequency and temperature has been simulated and is shown in Figure 4. For the heating process described in Figure 4a, we can see that the weak Fano 1 can be excited at around 60 \({}^{\circ}\)C. With the increasing temperature, Fano 2 is also excited and the resonance intensity is gradually strengthened. When the metadevice is heated to 70 \({}^{\circ}\)C, the intensity of Fano resonance reaches the maximum. Simultaneously, the simulated results given in Figure 4b describe the continuous tunability of Fano resonance better by using the cooling process.