Unlocking the -factor limit of topologically protected photonic bound states in the continuum in all-dielectric terahertz metasurfaces
Phys. Rev. Applied 24, 014039 – Published 21 July, 2025
DOI: https://doi.org/10.1103/3r2g-8xxt
Abstract
Photonic bound states in the continuum (BICs), possessing two unique properties of infinitely high quality () factor and momentum-space polarization vortex, promise unprecedented opportunities for tailoring high- resonances and enhancing light field manipulation. Recently, all-dielectric metasurfaces (MSs) underpinned by high refractive index and low intrinsic loss materials have unlocked the full potentials of BICs to realize ultrahigh- resonances. However, experimental demonstrations of high- terahertz BICs resonances in all-dielectric MSs with substrates remain a long-standing challenge. Here we propose and fabricate a paradigm of a crystalline silicon terahertz MS over a quartz substrate to demonstrate optical resonators with high- quasi-BICs resonances. These resonators feature the simultaneous excitation of multiple topologically protected symmetry-protected BICs and accidental BICs. Under larger asymmetries, two additional BICs are observed in symmetry-broken terahertz MSs, thereby offering an extra degree of freedom for engineering BICs and easing fabrication. Our experimental results reveal two quasi-BICs modes characterized by sharp Fano resonances that boast an unparalleled factor of up to 265, which is the highest reported experimental factor in a terahertz MS with a substrate. We envision that these findings will not only hold enormous prospects for broadening the functional scope of terahertz metaphotonics but will also lay the groundwork for the realization of high-performance terahertz optoelectronic devices and metadevices.
