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<p>Chiral metasurfaces leveraging bound states in the continuum (BICs) offer a powerful route for enhancing light–matter interactions. However, existing quasi-BIC architectures typically face a fundamental trade-off between high quality (Q) factors and wide-angle chiral operation. Most designs confine strong circular dichroism (CD) to isolated points in momentum space (k-space) and often rely on intricate three-dimensional (3D) meta-atoms, rendering them highly sensitive to fabrication imperfections and angular misalignment. Here, we experimentally realize a planar dielectric metasurface that supports a wide k-domain chirality arising from accidental BICs with a net zero-topological-charge (ZTC). By lifting a Dirac-type degeneracy through controlled in-plane and out-of-plane symmetry breaking, we induce a deterministic topological evolution in which the same-handed circularly polarized (C) points migrate toward and accumulate near the Γ point, while the opposite-handed singularities annihilate or shift to higher k-space. This mechanism delivers record-level performance—an ultrahigh Q-factor (~ 10<sup>4</sup>), near-unity linear and nonlinear CD (0.99/0.999), and robust angular coverage (|<i>k</i><sub><i>x</i></sub><i>P</i>/2π, <i>k</i><sub><i>y</i></sub><i>P</i>/2π|&lt; 0.06)—all within a fabrication-friendly, single-layer dielectric platform. These results establish a new regime for chiral photonics, unifying high chiral purity, angular robustness, and topological stability in a scalable planar architecture.</p>

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Robust chirality via merging accidental BICs with net zero topological charge

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月19日

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  • Hui Hu,
  • Chaobiao Zhou,
  • Yukang Zhang,
  • Meng-Xia Hu,
  • Juntian Peng,
  • Huawei Tang,
  • Lujun Huang,
  • Jianlong Liu,
  • Chunying Guan,
  • Zheng Zhu,
  • Xiaoshuang Chen,
  • Wei Lu,
  • Xiangping Li,
  • Zi-Lan Deng,
  • Guanhai Li,
  • Jinhui Shi,
  • Cheng-Wei Qiu

摘要

Chiral metasurfaces leveraging bound states in the continuum (BICs) offer a powerful route for enhancing light–matter interactions. However, existing quasi-BIC architectures typically face a fundamental trade-off between high quality (Q) factors and wide-angle chiral operation. Most designs confine strong circular dichroism (CD) to isolated points in momentum space (k-space) and often rely on intricate three-dimensional (3D) meta-atoms, rendering them highly sensitive to fabrication imperfections and angular misalignment. Here, we experimentally realize a planar dielectric metasurface that supports a wide k-domain chirality arising from accidental BICs with a net zero-topological-charge (ZTC). By lifting a Dirac-type degeneracy through controlled in-plane and out-of-plane symmetry breaking, we induce a deterministic topological evolution in which the same-handed circularly polarized (C) points migrate toward and accumulate near the Γ point, while the opposite-handed singularities annihilate or shift to higher k-space. This mechanism delivers record-level performance—an ultrahigh Q-factor (~ 104), near-unity linear and nonlinear CD (0.99/0.999), and robust angular coverage (|kxP/2π, kyP/2π|< 0.06)—all within a fabrication-friendly, single-layer dielectric platform. These results establish a new regime for chiral photonics, unifying high chiral purity, angular robustness, and topological stability in a scalable planar architecture.