Unidirectional plasmonic Bragg reflector based on longitudinally asymmetric nanostructures**Project supported by the Shenzhen Research Foundation, China (Grant Nos. JCYJ20160608153308846, JSGG20170822093953679, and JCYJ20180507182444250), the National Key Research and Development Program of China (Grant No. 2017YFC0803506), the National Natural Science Foundation of China (Grant Nos. 61261033 and 61162007), and the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 20160320).

Abstract

Plasmonic Bragg reflectors are essential components in plasmonic circuits. Here we propose a novel type of plasmonic Bragg reflector, which has very high reflectance for the right-side incidence and meanwhile has extremely large absorption for the left-side incidence. This device is composed of longitudinally asymmetric nanostructures in a metal–insulator–metal waveguide. In order to efficiently analyze, design, and optimize the reflection and transmission characteristics of the proposed device, we develop a semi-analytic coupled-mode model. Results show that the reflectance extinction ratio between plasmonic modes incident from the right-side and the left-side reaches 11 dB. We expect this device with such striking unidirectional reflection performance can be used as insulators in nanoplasmonic circuits.