Inhomogeneous metasurfaces have shown possibilities for unprecedented control of wave propagation and scattering. While it is conventional to shine a single incident plane wave from one side of these metastructures, illuminating by several waves simultaneously from both sides may enhance possibilities to control scattered waves, which results in additional functionalities and novel applications. Here, we unveil how by using coherent plane-wave illumination of a properly designed inhomogeneous metasurface sheet it is possible to realize controllable retroreflection. We call these metasurfaces “coherent retroreflectors” and explain the method for realizing them both in theory and in practice. We show that coherent retroreflectors can be used for filtering undesired modes and creation of field-localization regions in waveguides. The latter application is in resemblance to bound states in the radiation continuum.

中文翻译：

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相干逆反射超表面

非均匀超表面显示出前所未有的控制波传播和散射的可能性。虽然传统上从这些超结构的一侧照射单个入射平面波，但同时从两侧照射多个波可能会增加控制散射波的可能性，从而产生额外的功能和新颖的应用。在这里，我们揭示了如何通过使用适当设计的非均匀超表面片的相干平面波照明来实现可控的回射。我们将这些超表面称为“相干回射器”，并在理论和实践中解释了实现它们的方法。我们表明相干后向反射器可用于过滤不需要的模式并在波导中创建场定位区域。