Self-activated nonreciprocal transmission isolation via absorption-asymmetry-triggered directional phase transition in VO2-based terahertz metamaterials

Abstract

This study theoretically and numerically establishes a novel strategy for self-activated nonreciprocal transmission isolation in terahertz metamaterials, exploiting the absorption asymmetry of a vanadium dioxide (VO₂)-based structure to trigger directional phase transition under high-intensity illumination. Through coupled electromagnetic-thermal simulations, we analyze a tri-layer design where asymmetric absorption at specific frequencies—depending on incidence direction—induces markedly different thermal profiles. Crucially, high-intensity waves incident from the VO₂ side generate sufficient absorption-induced heating to surpass the phase transition threshold locally. This self-triggered phase change drastically suppresses transmission selectively for this direction, while waves incident from the opposing side experience significantly lower absorption and heating, maintaining high transmission. This fundamental asymmetry in thermal response enables nonreciprocal isolation without external excitation. Additionally, the transmission and absorption spectra are analyzed and the influences of absorption asymmetry, irradiation duration, incident power, and polarization direction are also investigated. This work demonstrates that harnessing absorption asymmetry to directionally control phase transition establishes a new paradigm for achieving nonreciprocal electromagnetic wave manipulation.