Metasurface leverages quasi-bound states in the continuum to tune photonic resonances

In nanophotonics, optical metasurfaces have shown promise for high-sensitivity sensing, multi-wavelength switching, and slow-light applications. However, multiple challenges exist in developing an efficient and compact optical platform for manipulating light at such a scale. New work in quasi-bound states in the continuum (qBICs) looks to address these issues.

Bound states in the continuum are ideal quantum states that don’t radiate, but in the real world, these interact with other materials and transition into qBICs. Shi et al. have theoretically demonstrated a polarization-dependent qBIC platform that supports multiple resonances. Based on symmetry-engineered silicon metasurfaces, the group’s proposed device modulates resonance by adjusting the polarization state of incident light. They examined the physical origins of the qBICs using electromagnetic field distributions and multipole decompositions.

“This work theoretically demonstrates a polarization-dependent metasurface that supports multiple high-quality-factor qBIC resonances and electromagnetically-induced transparency (EIT)-like features, enabling advanced manipulation of light at the nanoscale,” said author Bin Tang. “It opens up new pathways toward compact, multifunctional photonic devices — including ultra-sensitive optical sensors, multi-band switches with high modulation depths, and efficient slow-light modules — and thus moves the metasurface field closer to real-world integrated applications.”

Conventional metasurfaces often suffer from limited light-matter interaction strengths, narrow operational bandwidth, and restricted resonance tunability.

In contrast, the group’s metasurface theoretically demonstrates a strong coupling between its qBIC resonant modes, producing pronounced EIT-like effects with a remarkably high group-velocity index of approximately 39,000 — far above the tens to hundreds achieved in conventional designs — indicating its ability to modulate slow light. It also exhibits excellent sensing performance and enables high-contrast polarization-dependent optical switching.

The group hopes their work stimulates further innovation in integrated quantum photonic circuits, on-chip optical signal processing, and high-precision sensing, providing a fresh perspective toward multifunctional and ultra-compact photonic systems.

Source: “Symmetry-engineered dielectric metasurfaces for polarization-dependent quasi-BIC modes with reconfigurable optical responses,” by Deguo Shi, Jing Chen, Zongli Hu, Jialing Shi, and Bin Tang, Journal of Applied Physics (2025). The article can be accessed at https://doi.org/10.1063/5.0297379 .