Photo-imprinted Controllable Fano Resonance in the Terahertz Regime

The emergence of metamaterials, including the recently proposed metasurfaces, provides unprecedented opportunities in the manipulation as well as the generation of terahertz (THz) waves. Various actively controllable THz devices such as optical switches and phase modulators have been achieved by incorporating external-stimuli-responsive media (typically semiconductors) in the configurations. Compared to predesigned metallic-resonator-based metamaterials, photoimprinted photonic structures offer us an all-optical route toward reconfigurable functionalities with superior flexibility. Here, we propose to photoimprint some specific patterns on a thin film of semiconductor to excite Fano-like resonances, which result from the coupling between dark and bright elements. Experimental measurements, performed with THz time-domain spectroscopy, demonstrate counterintuitive tunable deep features in extinction spectra positioned around the expected resonance frequency. Our simulations are in excellent agreement with the experiments, by resembling realistic conditions of low contrast photoimprinted patterns generated with a spatial light modulator and a finite detection time window. This work takes the first step toward realizing switchable Fano resonances via an all-optical approach and, therefore, paves the way to more versatile manipulations of THz waves.