Dielectric Fourier metasurfaces—thin layers of strongly refracting transparent materials with periodic surface nanoreliefs—are capable of versatile flat-optical functionalities, including anomalous refraction in up to near-grazing directions. Describing the reliefs by a few Fourier coefficients, one can straightforwardly optimize them numerically or, eventually, analytically in terms of the Rayleigh hypothesis. We demonstrate that silicon Fourier metasurfaces supporting anomalous refraction in near-grazing directions can be employed as efficient optical Y-junction switches. Operating in the vicinity of a certain diffraction order cutoff, they can drastically alter the direction of outgoing light due to subtle variations of the optical setup. As examples, we show the possibility to deflect 70%–80% of the power of green light by more than 150 degrees when the incoming beam is inclined by only 2 degrees, or when the relative substrate permittivity is varied by 0.1. We also evaluate the prospects of metasurfaces made of other weaker-refracting transparent materials.

介电傅立叶超表面——具有周期性表面纳米浮雕的强折射透明材料的薄层——能够实现多种平面光学功能，包括在近掠射方向上的异常折射。用几个傅立叶系数描述浮雕，可以直接在数值上优化它们，或者最终根据瑞利假设进行分析。我们证明了支持近掠射方向异常折射的硅傅立叶超表面可以用作有效的光学 Y 结开关。在某个衍射级截止附近运行，由于光学设置的细微变化，它们可以极大地改变出射光的方向。作为例子，我们展示了当入射光束仅倾斜 2 度或相对基板介电常数变化 0.1 时，可以将 70%–80% 的绿光功率偏转 150 度以上。我们还评估了由其他弱折射透明材料制成的超表面的前景。