Structure-based tunable metamaterials for electromagnetically induced transparency windows in low terahertz frequency

The electromagnetically induced transparency (EIT) metamaterials with active or passive modulation have been extensively studied and applied in slow-light devices, light on-off, and light storage. However, the preparation complexity and characterization difficulties of the EIT metamaterials limit their optoelectronic applications. Here, we have employed a structure-based tunable design to fulfill the passive modulation of EIT metamaterial. We propose a simple but effective EIT structural model composed of a cutting wire and two circular split rings. Through theoretical analysis and computational simulation, it is found that the localized surface plasma and the inductive-capacitive resonance mode coincidently contribute to the EIT effect, giving rise to a narrow transparency window. Moreover, the amplitude of the transparency peak gradually decreases at the same resonance frequency with the increment of the lateral distance between the wire and split ring, while it decreases proportionally with the increment of the radius of the split ring. Interestingly, when the radius continues to increase, the asymmetry of the EIT window aggravates and the second EIT broad transparency window appears, indicating the existence of another intriguing coupling mechanism. Our work unveils a simple and practical modulation strategy for EIT-based multifunctional optical devices and shed light on its potential application on the optical devices.