Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 USA.
Phys Rev Lett. 2019 Mar 22;122(11):113901. doi: 10.1103/PhysRevLett.122.113901.
Metasurfaces allow tailored control of electromagnetic wave fronts. However, due to local conservation of power flow, passive, lossless, and reflectionless metasurfaces have been limited to imparting phase discontinuities-and not power density discontinuities-onto a wave front. Here, we show how the phase and amplitude profiles of a wave front can be independently controlled using two closely spaced phase-discontinuous metasurfaces. The two metasurfaces, each designed to exhibit spatially varying refractive properties, are separated by a wavelength-scale distance and together form a compound metaoptic. A method of designing the compound metaoptic is presented, which enables transformation between arbitrary complex-valued field distributions without reflection, absorption, polarization loss, or active components. Such compound metaoptics may find applications in the optical trapping of particles, displaying three-dimensional holographic images, shrinking the size of optical systems, or producing custom (shaped and steered) far-field radiation patterns.
超表面能够实现对电磁波波前的精细控制。然而，由于局部功率流守恒，无源、无损耗、无反射的超表面只能在波前上引入相位不连续，而不是功率密度不连续。在这里，我们展示了如何使用两个紧密间隔的相位不连续超表面来独立控制波前的相位和幅度分布。这两个超表面，每个都设计成具有空间变化的折射特性，通过一个波长量级的距离隔开，并共同形成一个复合超构光学元件。提出了一种设计复合超构光学元件的方法，该方法能够在不反射、吸收、偏振损耗或使用有源元件的情况下，在任意复值场分布之间进行变换。这种复合超构光学元件可应用于粒子的光学捕获、显示三维全息图像、缩小光学系统的尺寸或产生定制（形状和转向）的远场辐射模式。
