Coupled thermal–optical–structural dynamics enable nonlinear limiting in mid-infrared VO₂/SiO₂ films

Optical limiting in the mid-infrared regime is a key functionality for next-generation photonic protection and sensing systems, yet the underlying response mechanisms of phase-transition materials in this spectral range remain poorly understood. Here, we report a VO₂/SiO₂ heterostructure that exhibits self-regulated optical limiting under continuous-wave (CW) excitation at 3.8 μm. In this system, the optical transmission, thermal evolution, and structural phase transition are strongly coupled. Through real-time dual-band measurements, we uncover a characteristic four-stage dynamical pathway, comprising a thermal-inertia response, a threshold-activated insulator–metal transition (IMT), a saturated optical-limiting regime, and a spontaneous cooling recovery. Importantly, we identify that at the limiting threshold, the thermal diffusion pathway shifts from predominantly lateral heat accumulation to vertically focused conduction. This shift emerges as the critical mechanism governing the onset of the optical limiting response. Through the integration of in situ spectral inversion and multiphysics simulations, we construct a predictive thermo-optical model that captures the coupled dynamics of phase transition. The findings not only elucidate the physical mechanisms underlying VO₂-based optical limiting in the mid-infrared, but also provide a theoretical basis for the design of next-generation optical limiting devices.