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Planar gradient metamaterials

Abstract

Metamaterials possess exotic properties that do not exist in nature. Gradient metamaterials, which are characterized by a continuous spatial variation of their properties, provide a promising approach to the development of both bulk and planar optics. In particular, planar gradient metamaterials can be classified into three categories: gradient metasurfaces, gradient index metamaterials and gradient metallic gratings. In this Review, we summarize the progress made in the theoretical modelling of these materials, in their experimental implementation and in the design of functional devices. We discuss the use of planar gradient metamaterials for wave bending and focusing in free space, for supporting surface plasmon polaritons and for the realization of trapped rainbows. We also focus on the implementation of these materials in waveguide systems, which can enable electromagnetic cloaking, Fano resonances, asymmetric transmission and guided mode conversion. Finally, we discuss promising trends, such as the use of dielectric rather than metallic unit elements and the use of planar gradient metamaterials in 3D systems.

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Figure 1: Different planar gradient metamaterials for the manipulation of electromagnetic waves in free space.
Figure 2: Experimental realizations of bending and focusing (or emitting) waves based on planar gradient metamaterials.
Figure 3: Planar gradient metamaterials for manipulating surface plasmon polaritons.
Figure 4: Novel phenomena in waveguide structures with GIMs.
Figure 5: Experimental demonstrations of waveguide structures with planar gradient metamaterials.

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Acknowledgements

This work was supported by the National Science Foundation of China for Excellent Young Scientists (grant no. 61322504), the Postdoctoral Science Foundation of China (grant no. 2015M580456), the National Excellent Doctoral Dissertation of China (grant no. 201217), and the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions. The authors thank Winsley Yang for proofreading.

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Correspondence to Huanyang Chen.

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Xu, Y., Fu, Y. & Chen, H. Planar gradient metamaterials. Nat Rev Mater 1, 16067 (2016). https://doi.org/10.1038/natrevmats.2016.67

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