Reversible Switching of Slow-Photon-Enhanced Light Absorption by Dynamic Collapse of Photonic Band-Edge Localization

Abstract Dynamic control of light–matter interactions is a fundamental requirement for active photonics, enabling adaptive optical devices and information processing, copackaged optics, and reconfigurable photonic materials. While active photonic crystals can reversibly tune photonic bandgap positions, modulation of electromagnetic field localization in photonic structures has remained elusive. Here, we demonstrate electrochemical switching of light–matter interactions and field localization in a hierarchical titanium oxide nanotube material combining subwavelength in-plane structuring with wavelength-scale out-of-plane photonic ordering. In the activated state, the advanced material supports band-edge electromagnetic field localization, facilitating enhanced optical absorption based on the slow-photon effect. By electrochemical lithiation, the refractive-index contrast of the hierarchical structure is reduced, reversibly driving a transition from a photonic crystal architecture supporting band-edge localization to an effective-medium regime in which field localization and slow-photon-assisted absorption are suppressed. The experimentally observed optical response and the reversible switching mechanism are further supported by full-wave simulations. These results establish dynamic control of photonic band-edge localization as a strategy for reversibly manipulating light–matter interactions in adaptive photonic materials.