Bianisotropy is a powerful concept enabling asymmetric optical response, including asymmetric reflection, absorption, optical forces, light trapping, and lasing. The physical origin of these asymmetric effects can be understood from magnetoelectric coupling and asymmetrical field enhancement. Here, we theoretically propose highly asymmetric second-harmonic generation in bianisotropic AlGaAs metasurfaces. We show that the ratio of second-harmonic power for the forward and backward illuminations can be increased by around four orders of magnitude. This effect is obtained by altering geometrical parameters that coincide with quasi-bound states in the continuum. Our study paves the way toward a directional generation of higher-order waves and can be potentially useful for nonlinear holograms.

中文翻译：

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基于连续体中束缚态的双各向异性超表面中的巨大不对称二次谐波产生

双向异性是一个强大的概念，可以实现非对称光学响应，包括非对称反射、吸收、光学力、光捕获和激光。这些不对称效应的物理起源可以通过磁电耦合和不对称场增强来理解。在这里，我们从理论上提出了在双各向异性 AlGaAs 超表面中产生高度不对称的二次谐波。我们表明，前向和后向照明的二次谐波功率比可以增加大约四个数量级。这种效果是通过改变与连续体中准束缚态一致的几何参数来获得的。我们的研究为定向生成高阶波铺平了道路，并且可能对非线性全息图有用。