Nonlinear optics has generated a wide range of applications in the fields of optical communications, biomedicine, and materials science, with nonlinear conversion efficiency serving as a vital metric for its progress. However, the weak nonlinear response of materials, high optical loss, and inhomogeneous distribution of the light field hamper the improvement of the conversion efficiency. We present a composite grating waveguide structure integrated into a Bragg reflector platform. This design achieves high Q in the spectral range by exploiting the unique properties exhibited by the bound states in the Bloch surface wave-enhanced continuum, and efficient second-harmonic generation by close-field amplification with the optical field tightly localized in a nonlinear material. By manipulating the symmetry of the grating, a precise tune over the near field within a designated wavelength range can be achieved. Specifically, we select a photonic crystal configuration supporting surface waves, employing TE polarization conditions and an asymmetry factor of −0.1 between the composite gratings. This configuration resonates at a fundamental wavelength of 783.5 nm, exhibiting an impressive Q-factor of 106. Notably, at an incident light intensity of 1.33 GW/cm2, we achieve a normalized electric field strength of up to 940 at the fundamental frequency and a second-harmonic conversion efficiency of up to 6 × 10−3, significantly amplifying the second-harmonic response. The proposed configuration in this investigation has the potential to be integrated into the field of nonlinear optics for sensing frequency conversion applications.

中文翻译：

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布洛赫表面波增强铌酸锂薄膜连续体准束缚态的高效二次谐波产生

非线性光学在光通信、生物医学、材料科学等领域有着广泛的应用，非线性转换效率是衡量其进步的重要指标。然而，材料的非线性响应弱、光损耗高、光场分布不均匀等问题阻碍了转换效率的提高。我们提出了一种集成到布拉格反射器平台中的复合光栅波导结构。该设计通过利用布洛赫表面波增强连续体中的束缚态所表现出的独特特性，以及通过近场放大（光场紧密局域于非线性材料中）来高效产生二次谐波，在光谱范围内实现了高Q值。通过操纵光栅的对称性，可以实现指定波长范围内近场的精确调谐。具体来说，我们选择支持表面波的光子晶体配置，采用 TE 偏振条件和复合光栅之间的不对称系数为 -0.1。这种配置在 783.5 nm 的基本波长处共振，表现出令人印象深刻的问- 10 的因数6。值得注意的是，在 1.33 GW/cm2 的入射光强度下2，我们在基频下实现了高达 940 的归一化电场强度和高达 6 × 10 的二次谐波转换效率−3，显着放大二次谐波响应。本研究中提出的配置有可能集成到非线性光学领域，用于传感频率转换应用。