A multifunctional terahertz device based on vanadium dioxide metamaterials that switches between ultra-broadband absorption and ultra-high-Q narrowband absorption

Abstract

Terahertz absorbers with ultra-broadband and ultra-narrowband absorption capabilities are crucial for integrated and efficient terahertz modulation. This paper proposes a dual-mode tunable terahertz absorber based on the phase transition characteristics of vanadium dioxide (VO2), enabling dynamic switching between narrowband and broadband absorption through its insulating-to-metallic transition. In the insulating state, the excitation of quasi-bound states in the continuum (Q-BIC) resonance via geometric parameter modulation of silicon pillars is investigated, with its physical mechanism elucidated through impedance matching theory and multipole analysis. This mode demonstrates exceptional sensing performance at 8.017 THz: a refractive index sensitivity of 3.735 THz/RIU, a quality factor (Q) of 4800.89, and a figure of merit (FOM) reaching 3822.93 RIU-1. When VO₂ is transformed into the metallic state, the device achieves more than 90% ultra-broadband absorption in the range of 3.93 THz to 9.25 THz, and its broadband absorption property originates from the electric dipole resonance. In addition, the effect of material structural parameters on the broadband absorption performance was investigated, and it was found that the performance of the device remained stable when different structural parameters were used. Compared to existing technologies, this design integrates dual functionalities in a single-layer hybrid structure, significantly reducing fabrication complexity. It provides novel insights for terahertz sensing, environment-adaptive devices, and multifunctional photonic chips.