Abstract
Synthesization of multiple functionalities over a flat metasurface platform offers a promising approach to achieving integrated photonic devices with minimized footprint. Metasurfaces capable of diverse wavefront shaping according to wavelengths and polarizations have been demonstrated. Here we propose a class of angle-selective metasurfaces, over which beams are reflected following different and independent phase gradients in the light of the beam direction. Such powerful feature is achieved by leveraging the local phase modulation and the non-local lattice diffraction via inverse scattered field and geometry optimization in a monolayer dielectric grating, whereas most of the previous designs utilize the local phase modulation only and operate optimally for a specific angle. Beam combiner/splitter and independent multibeam deflections with up to 4 incident angles are numerically demonstrated respectively at the wavelength of 700 nm. The deflection efficiency is around 45% due to the material loss and the compromise of multi-angle responses. Flexibility of the approach is further validated by additional designs of angle-switchable metagratings as splitter/reflector and transparent/opaque mirror. The proposed designs hold great potential for increasing information density of compact optical components from the degree of freedom of angle.
Highlights
Driven by the continuous demand of system integration and device minimization, incorporating more and more functionalities in a single metasurface platform is highly demanding
To bypass the single phase gradient functionality imparted by the local phase approximation, we choose an alternative metasurface design methodology based on inverse numerical optimization techniques
When a constant phase gradient ξ is introduced by the metasurface at the interface, beams coming into and out of the metasurface are governed by the generalized law of reflection[37], known as the grating equation[39]: k0(sinθr − sinθi) = ξ where k0 is the wavevector in vacuum, and θi and θr are angles of incidence and reflection
Summary
Driven by the continuous demand of system integration and device minimization, incorporating more and more functionalities in a single metasurface platform is highly demanding. Multifunctional metasurfaces aiming at dual/multi frequency bands or with polarization-selective features have been extensively studied[17,18,19,20,21] They rely on spatial multiplexing of different subarrays, either in-plane[17,18,19] or layered[20,21], in a shared aperture with each subarray imparting a specific phase map. The phase shifters are designed to provide a desired phase gradient for a specific incident direction (e.g. normal excitation), they show the same phase gradient for a wide range of incident angles (around normal direction)[37,38] This phenomenon is favorable for wide-view applications, but on the other hand limits the freedom of angular selectivity, and forces waves from different directions to follow the same deflection rule. This study is focused on one-dimensional reflection engineering, the angle-selective concept is general and extensible to two-dimensional deflection in either reflection or transmission side by optimizing two-dimensional gratings
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