## 5 Analysis of Physical Mechanism
Hence, THz photon energy can be strongly restricted in the MMs through diffraction coupling, which greatly enhances the energy stored in the subwavelength resonant unit. Based on the above analysis, the incident THz photon energy is strongly bounded in the MMs and the radiation damping is suppressed by the cancellation interference of electric dipole, which leads to the extremely high Q-factor of Fano 2. To further optimize the Q-factor and modulation depth of the Fano resonances, we study the influence of asymmetric parameters on the spectral response. Figure 6a,b show one- and two-dimensional graphs of the simulated THz transmission spectra corresponding to different asymmetric parameters (offset length \(a\)), respectively. It can be seen that when the offset length is 0 \(\upmu\)m, i.e. the symmetrical double C-shaped structure is presented, we can only observe the eigen resonance excited by dipole resonance in the whole transmission spectrum, as the dark blue curve shown in Figure 6a. As expected, the increasing offset length breaks the symmetry of the structure, inducing the resonances of Fano 1 and Fano 2 on both sides of the eigen resonance. Interestingly, the increasing offset length makes the eigen resonance mode move to the high frequency range (the blue shift), while the excited Fano 1 and Fano 2 shift to the low frequency (the red shift). The resonance linewidth is gradually widened and the resonance dip is significantly attenuated. Figure 6: Transmission spectra of the VO\({}_{2}\)-implanted MM structures for different asymmetric parameters (offset length) at high temperature (70 \({}^{\circ}\)C): (**a**) one-and (**b**) two-dimensional graphs. Using the surface current and electric field distributions in Figure 5, we can easily understand the influence of offset length on the resonant spectrum. For the eigen resonance, the electric field intensity is mainly coupled to the C-shaped structure on the right side, while the corresponding electric field intensities of Fano 1 and Fano 2 are mainly distributed on the right-side C-shaped structure. Therefore, the increase of offset length results in the extension of the left geometrical length and the reduction of the right side. The arm length is inversely proportional to the response frequency in MMs, which produces different resonant modes [42]. We analyze the relationship between the Q-factor and modulation depth of Fano 1 and Fano 2 with the offset length, as shown in Figure 7a,b. Although obtaining the maximum Q-factor and the modulation depth at the same time is the pursuit of many device applications, there is a significant trade-off between the Q-factor and the modulation depth of these two Fano resonances. For Fano 1, as the offset length changes from 3 \(\upmu\)m to 30 \(\upmu\)m, the Q-factor drops sharply from 33 to 4 while the modulation depth increases rapidly from 63.5% to 99.4%, as shown in Figure 7a. For Fano 2, as long as a small offset length is introduced, Fano 2 will appear immediately and the Q-factor is up to 98 while the modulation depth is only 16.5%, as shown in Figure 7b. It should be noted that Fano 1 and Fano 2 are dark modes that cannot be obtained in symmetry structure and they only appear when symmetry of structure is destroyed. Changing the asymmetric parameter will not lead to the essential change of these two resonances, but will greatly affect their Q-factor and modulation depth. To reflect the superior performance of the proposed active switching, we provide a clear comparison between the parameters of designed metadevice with others previously reported experimentally and numerically among the literature [18; 19; 43; 44], including THz metamaterial type, type of switching, resonance frequency, Q factor and modulation depth, the results are shown in Table 1. It can be seen that compared with the VO\({}_{2}\) implanted THz MMs, the graphene, photosensitive silicon and MEMS MMs can also be employed to realize the switching behaviors of Fano resonance.