Low-Contrast BIC Metasurfaces with Quality Factors Exceeding 100,000

TL;DR

This paper reports the experimental realization of low-contrast silicon-based BIC metasurfaces achieving record-high Q factors over 100,000, enabling ultra-sensitive environmental sensing and advancing high-Q optical device applications.

Contribution

Demonstrated ultrahigh-Q BIC metasurfaces using low-contrast silicon pairs, overcoming fabrication limitations and enabling stable, high-sensitivity optical sensing.

Findings

Achieved a Q factor of 101,486 in BIC metasurfaces.

Demonstrated sub-picometer wavelength stability in water.

Detected environmental refractive index changes at 10^{-5} level.

Abstract

Dielectric metasurfaces operating at quasi-bound states in the continuum (qBICs) can achieve exceptionally high radiative quality ($\textit{Q}$) factors by introducing small asymmetries into their unit cells. However, fabrication imperfections often impose major limitations on the experimentally observed $\textit{Q}$ factors. In this study, we experimentally demonstrate BIC metasurfaces with a record-high $\textit{Q}$ factor of 101,486 under normal excitation of light in the telecom wavelength range achieved by employing low-contrast silicon pairs. Our findings show that such ultrahigh-$\textit{Q}$ factors can be attained by leveraging both the high radiative $\textit{Q}$ factors of higher-order qBIC modes and reduced scattering losses in shallow-etched designs. Additionally, we demonstrate stable sub-picometer-level wavelength fluctuations in water, with a limit of detection of $10^{-5}$ for environmental refractive index changes. The proposed approach can be extended to BIC metasurfaces with many other configurations and operating wavelengths for ultrahigh-$\textit{Q}$ applications in both fundamental physics and advanced devices.