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Front. Phys. | doi: 10.3389/fphy.2019.00161

Tunable unidirectivity of metal-dielectric-metal plasmonic nanoantennas with PT-symmetric potentials

 Chaowei Xu1, 2, Kaiyang Cheng1, 2, Xiaobing Shang2, 3, Quan Li1, 2,  Zeyong Wei1, 2, Chao Wu1, 2, Xiaoming Zhang4* and Hongqiang Li1, 2*
  • 1School of Physical Science and Engineering, Tongji University, China
  • 2Institute of Dongguan-Tongji University, China
  • 3School of Electronics and Information Engineering, Tongji University, China
  • 4College of Physics Science and Engineering Technology, Yichun University, China

Parity-time (PT) symmetric photonic systems have attracted much attention due to their intriguing properties and asymmetric behaviors. In this paper, we propose a plasmonic nanoantenna with PT-symmetric potential for unidirectional scattering functionality. The studied plasmonic nanoantenna is comprised of three metallic layers separated by two dielectric layers. Such kind of system, with the same coefficient of loss and gain in each of the two dielectric layers, holds the characteristic of PT symmetry. We show that the unidirectional scattering is obtained for the passive structure (i.e. κ=0, ), and the switching between forward and backward directionality can be achieved with a single element by changing the excitation wavelength, when the induced electric dipole (ED) and magnetic dipole (MD) modes satisfy the first or second Kerker conditions, respectively. In addition, we find that the forward-to-backward ratio spectra can be strongly affected by the non-Hermiticity parameter κ. In particular, it is possible to reverse the radiation direction at the same wavelength in a wide spectra band by adjusting κ. Moreover, putting the nanoantennas in an array of transverse configuration can efficiently narrow the main lobe angular beam width to be less than 6 degrees . These results contribute to the basic understanding of the optical properties of active-passive finite nanostructures with potential applications for the design of novel nanostructures displaying asymmetric and tunable responses.

Keywords: optical nanoantenna, metallic and dielectric hybrid, parity-time symmetric, tunable, unidirectional scattering, Kerker condition

Received: 16 Jul 2019; Accepted: 04 Oct 2019.

Copyright: © 2019 Xu, Cheng, Shang, Li, Wei, Wu, Zhang and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. Xiaoming Zhang, College of Physics Science and Engineering Technology, Yichun University, Yichun, China, zhangxm@163.com
Prof. Hongqiang Li, School of Physical Science and Engineering, Tongji University, Shanghai, China, hqlee@tongji.edu.cn