Zhong Hongkun, He Tiantian, Wang Yuhao, Qi Tiancheng, Meng Yuan, Li Dan, Yan Ping, Xiao Qirong
Opt Express. 2024 Feb 12;32(4):5862-5873. doi: 10.1364/OE.515896.
Bound states in the continuum (BIC) offer great design freedom for realizing high-quality factor metasurfaces. By deliberately disrupting the inherent symmetries, BIC can degenerate into quasi-BIC exhibiting sharp spectra with strong light confinement. This transformation has been exploited to develop cutting-edge sensors and modulators. However, most proposed quasi-BICs in metasurfaces are composed of unit cells with C symmetry that may experience performance degradation due to polarization deviation, posing challenges in practical applications. Addressing this critical issue, our research introduces an innovative approach by incorporating metasurfaces with C unit cell symmetry to eliminate polarization response sensitivity. Vanadium Dioxide (VO) is a phase-change material with a relatively low transition temperature and reversibility. Here, we theoretically investigate the polarization-insensitive quasi-BIC modulation in Si-VO hybrid metasurfaces. By introducing defects into metasurfaces with C, C, and C symmetries, we enable the emergence of quasi-BICs characterized by strong Fano resonance in their transmission spectra. Via numerically calculating the multipole decomposition, distinct dominant multipoles for different quasi-BICs are identified. A comprehensive investigation into the polarization responses of these structures under varying directions of linearly polarized light reveals the superior polarization-independent characteristics of metasurfaces with C and C symmetries, a feature that ensures the maintenance of maximum resonance peaks irrespective of polarization direction. Utilizing the polarization-insensitive quasi-BIC, we thus designed two different Si-VO hybrid metasurfaces with C symmetry. Each configuration presents complementary benefits, leveraging the VO phase transition's loss change to facilitate efficient modulation. Our quantitative calculation indicates notable achievements in modulation depth, with a maximum relative modulation depth reaching up to 342%. For the first time, our research demonstrates efficient modulation using polarization-insensitive quasi-BICs in designed Si-VO hybrid metasurfaces, achieving identical polarization responses for quasi-BIC-based applications. Our work paves the way for designing polarization-independent quasi-BICs in metasurfaces and marks a notable advancement in the field of tunable integrated devices.
连续域束缚态（BIC）为实现高品质因子超表面提供了极大的设计自由度。通过有意破坏固有对称性，BIC可退化为具有强光限制的尖锐光谱的准BIC。这种转变已被用于开发前沿传感器和调制器。然而，超表面中大多数提出的准BIC由具有C对称性的单元组成，可能会因偏振偏差而导致性能下降，这在实际应用中带来了挑战。为了解决这一关键问题，我们的研究引入了一种创新方法，通过将具有C单元对称性的超表面结合起来，以消除偏振响应敏感性。二氧化钒（VO）是一种具有相对较低转变温度和可逆性的相变材料。在此，我们从理论上研究了Si-VO混合超表面中的偏振不敏感准BIC调制。通过在具有C、C和C对称性的超表面中引入缺陷，我们使得在其透射光谱中出现以强法诺共振为特征的准BIC。通过数值计算多极分解，确定了不同准BIC的不同主导多极。对这些结构在不同线性偏振光方向下的偏振响应进行的全面研究揭示了具有C和C对称性的超表面具有卓越的偏振无关特性，这一特性确保无论偏振方向如何，最大共振峰都能保持。利用偏振不敏感准BIC，我们设计了两种具有C对称性的不同Si-VO混合超表面。每种配置都有互补的优点，利用VO相变的损耗变化来促进高效调制。我们的定量计算表明在调制深度方面取得了显著成果，最大相对调制深度达到342%。我们的研究首次证明了在设计的Si-VO混合超表面中使用偏振不敏感准BIC进行高效调制，为准BIC基应用实现了相同的偏振响应。我们的工作为在超表面中设计偏振无关准BIC铺平了道路，并标志着可调谐集成器件领域的一项显著进展。
