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<p>Conventional nonlinear chiral platforms suffer from limitations such as weak material responses and metal-induced losses. Achieving robust nonlinear chirality with high efficiency on etch-free lithium niobate (LN) platforms remains a critical challenge. In this work, we theoretically propose an etch-free silicon-lithium niobate (Si-LN) hybrid metasurface that leverages quasi-bound states in the continuum (quasi-BICs) to realize high-efficiency second-harmonic optical circular dichroism (SHOCD) in the near-infrared regime. By strategically breaking in-plane symmetry through the precise tuning of geometric parameters—namely, the asymmetry factor (α) and rotation angle (θ)—we engineer quasi-BIC resonances with adjustable quality factors, thereby enabling pronounced circular dichroism (CD) under both right- and left-circularly polarized (RCP/LCP) illumination. The proposed structure exhibits exceptional linear CD near quasi-BIC resonances and attains an outstanding SHOCD value of approximately ± 1. Notably, the second-harmonic (SH) conversion efficiency under RCP excitation exceeds that under LCP by two orders of magnitude, owing to ultrahigh quality factors (Q &gt; 10<sup>3</sup>) and polarization-selective field localization. Multipole decomposition analysis confirms that the giant chiral nonlinear response arises from the dominant contributions of the magnetic quadrupole (MQ) under RCP excitation and the magnetic dipole (MD) under LCP excitation. With an optimized SH conversion efficiency of ~ 2 × 10<sup>−3</sup> at a pump intensity of 50&#xa0;MW/cm<sup>2</sup>, this study presents a viable approach for developing high-performance nonlinear chiral devices on etch-free LN platforms, offering promising applications in quantum optics, chiral sensing, and integrated photonics.</p>

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High-efficiency second harmonic circular dichroism in etch-free Si-LiNbO3 hybrid metasurfaces via Quasi-bound states in the continuum

  • 期刊论文

  • 发表日期：

    2025年10月15日

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  • Zhijin Huang,
  • Junzhong Wang,
  • Kaixiang Shen,
  • Lifang Yuan

摘要

Conventional nonlinear chiral platforms suffer from limitations such as weak material responses and metal-induced losses. Achieving robust nonlinear chirality with high efficiency on etch-free lithium niobate (LN) platforms remains a critical challenge. In this work, we theoretically propose an etch-free silicon-lithium niobate (Si-LN) hybrid metasurface that leverages quasi-bound states in the continuum (quasi-BICs) to realize high-efficiency second-harmonic optical circular dichroism (SHOCD) in the near-infrared regime. By strategically breaking in-plane symmetry through the precise tuning of geometric parameters—namely, the asymmetry factor (α) and rotation angle (θ)—we engineer quasi-BIC resonances with adjustable quality factors, thereby enabling pronounced circular dichroism (CD) under both right- and left-circularly polarized (RCP/LCP) illumination. The proposed structure exhibits exceptional linear CD near quasi-BIC resonances and attains an outstanding SHOCD value of approximately ± 1. Notably, the second-harmonic (SH) conversion efficiency under RCP excitation exceeds that under LCP by two orders of magnitude, owing to ultrahigh quality factors (Q > 103) and polarization-selective field localization. Multipole decomposition analysis confirms that the giant chiral nonlinear response arises from the dominant contributions of the magnetic quadrupole (MQ) under RCP excitation and the magnetic dipole (MD) under LCP excitation. With an optimized SH conversion efficiency of ~ 2 × 10−3 at a pump intensity of 50 MW/cm2, this study presents a viable approach for developing high-performance nonlinear chiral devices on etch-free LN platforms, offering promising applications in quantum optics, chiral sensing, and integrated photonics.