## 3 Results and Discussion  
### Passive Modulation of Metamaterial EIT-like Window  
The EIT-like effect is caused by the coupling and destructive interference between the bright and dark eigenmodes [26,27], when the coupling distance changes, the coupling strength will change accordingly, leading to the modulation of the EIT-like effect. The influence of the distance \(\delta\) on the EIT window was investigated by varying the distance \(\delta_{x}\) between CW and USRs in the symmetric structure and the distance \(\delta_{y}\) between the upper and lower USRs. As shown in Figure 4a, the horizontal distance \(\delta_{x}\) between the CW and USRs was varied from 1 \(\upmu\)m to 17 \(\upmu\)m with the distance fixed \(\delta_{y}\) distance of 30 \(\upmu\)m to show the influence of the modulation effect of the transparent window. It can be found that when \(\delta_{x}\) is 1 \(\upmu\)m and 5 \(\upmu\)m, the electric field was mainly confined in the dark mode, which indicates that most of the energy of the bright mode CW had been coupled into the dark mode. As the relative distance \(\delta_{x}\) between the bright and dark modes increased, the coupling between the eigenmodes became weaker. The two resonance troughs of LSP resonance and LC resonance decreased and drew closer at the same time, with the transparent window blue-shifted. When \(\delta_{x}\) reached 17 \(\upmu\)m, the coupling disappeared completely, and the transparency window disappeared, too. While the influence of vertical distance \(\delta_{y}\)-, \(\delta_{x}\) was fixed as 4 \(\upmu\)m, the transparent window could be modulated by changing the \(\delta_{y}\) from 28 \(\upmu\)m to 12 \(\upmu\)m. It can be seen from Figure 4b that, when \(\delta_{y}\) = 28 \(\upmu\)m, the incident THz wave and CW were strongly coupled, and the dark mode was also excited by near-field coupling. As a result, the electric field in the bright mode was suppressed,  
Figure 3: The distribution of electromagnetic field and surface current corresponding to three different characteristic frequencies. **(a,b)** The electromagnetic field distribution at frequencies of 0.95 THz, 1.01 THz, 1.05 THz, and the coupling between the bright and dark mode at troughs of 0.95 THz and 1.05 THz are very weak; **(c)** The surface current distribution of symmetrical structure at different frequencies (the red arrow indicates the current direction), the current directions at the low-frequency trough are opposite, while at high-frequency trough are in the same direction; **(d–f)** The electromagnetic field distribution of asymmetric structure at three characteristic frequencies. therefore, a transparent window was found around 1 THz. As the USR pairs approached each other, the relative distance \(\delta_{y}\)- decreased, the coupling between eigenmodes was weakened, while the LC resonance troughs gradually disappeared. When \(\delta_{y}\) = 12 \(\upmu\)m, the induced magnetic fields caused by the surface currents of the two USR pairs suppressed each other, and the induced magnetic field regions were cancelled out, as a result, the dark mode could not be successfully excited, and the EIT-like window disappeared. Moreover, as seen from Figure 4, as \(\delta_{x}\) increased, the transparent window became narrower, which can be attributed to the reduced coupling of the CW and the USRs resonator. In contrast, when \(\delta_{y}\) was reduced from 28 \(\upmu\)m to 20 \(\upmu\)m, it was noticed that the influence was more of a frequency drift rather than changing the EIT window width. This behavior indicated that by changing the coupling between the bright and the dark modes, the EIT-like effect could be effectively modulated. For asymmetric structures, the horizontal position between the upper and lower asymmetric USRs were kept unchanged to investigate the influence of the distance \(\delta_{x}\) between CW and asymmetric USRs and the distance \(\delta_{y}\) between the upper and downer USRs on the EIT-like effects.