Enhanced robustness of high Q-factor chiral metasurface via Brillouin zone folding

Abstract

Chiral structures have broad applications in fields such as biosensing, chemistry, and nonlinear optics. However, in the design of chiral structures, it is also challenging to achieve a high circular dichroism (CD), high Q-factor and high robustness. In our study, we designed a metasurface based on α-Si, by inducting Brillouin zone folding we enhanced the Q-factor of BICs over a broad wavevector range. Specifically, by doubling the period of the unit structure of the metasurface, we enhanced the Q factors over a wide range via Brillouin zone folding. Furthermore, by breaking in-plane and out-of-plane symmetries of the structure, dual narrowband chiral functionalities were achieved. At the two resonance frequencies of 17.4808 THz and 17.4811 THz, CD values reached −0.94 and −0.93, with Q-factors as high as 3.7 × 10⁵, exhibiting strong robustness in both momentum and geometric spaces. Finaly, we investigated the physical mechanisms of CD and high-Q factors through band structure analysis and multipole decomposition. This work provides new insights into the design of chiral optical devices and offers potential benefits for improving the performance of biosensing and nonlinear optical devices.