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Experimental demonstration of a unidirectional reflectionless parity-time metamaterial at optical frequencies


Invisibility by metamaterials is of great interest, where optical properties are manipulated in the real permittivity–permeability plane1,2. However, the most effective approach to achieving invisibility in various military applications is to absorb the electromagnetic waves emitted from radar to minimize the corresponding reflection and scattering, such that no signal gets bounced back. Here, we show the experimental realization of chip-scale unidirectional reflectionless optical metamaterials near the spontaneous parity-time symmetry phase transition point where reflection from one side is significantly suppressed. This is enabled by engineering the corresponding optical properties of the designed parity-time metamaterial in the complex dielectric permittivity plane. Numerical simulations and experimental verification consistently exhibit asymmetric reflection with high contrast ratios around a wavelength of of 1,550 nm. The demonstrated unidirectional phenomenon at the corresponding parity-time exceptional point on-a-chip confirms the feasibility of creating complicated on-chip parity-time metamaterials and optical devices based on their properties.

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Figure 1: Characteristics of evolution of parity-time symmetry in the proposed passive parity-time metamaterial.
Figure 2: Optical properties of the designed passive unidirectional reflectionless parity-time metamaterial.
Figure 3: Experimental implementation of the passive unidirectional reflectionless parity-time metamaterial.
Figure 4: Measured optical properties of the parity-time metamaterial.


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We acknowledge critical support and infrastructure provided for this work by the Kavli Nanoscience Institute at Caltech. This work was supported by the NSF ERC Center for Integrated Access Networks (no. EEC-0812072), the National Basic Research of China (no. 2012CB921503 and no. 2013CB632702), the National Nature Science Foundation of China (no. 11134006), the Nature Science Foundation of Jiangsu Province (no. BK2009007), the Priority Academic Program Development of Jiangsu Higher Education, and CAPES and CNPQ—Brazilian Foundations. M-H.L. also acknowledges the support of FANEDD of China.

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Authors and Affiliations



L.F. and M-H.L. conceived the idea. L.F., Y-L.X. and M-H.L. designed the device. Y-L.X., L.F. and M-H.L. performed the theoretical analysis of parity-time symmetry. W.S.F. and L.F. designed the chip and carried out fabrications and measurements. All the authors contributed to discussion of the project. Y-F.C. and A.S. guided the project. L.F. wrote the manuscript with revisions from other authors.

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Correspondence to Liang Feng, Ye-Long Xu, William S. Fegadolli or Ming-Hui Lu.

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The authors declare no competing financial interests.

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Feng, L., Xu, YL., Fegadolli, W. et al. Experimental demonstration of a unidirectional reflectionless parity-time metamaterial at optical frequencies. Nature Mater 12, 108–113 (2013).

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