Nonreciprocal transmission in a nonlinear coupled heterostructure.

A nonlinear coupled heterostructure, metal-nonlinear-metal-insulator-metal, is proposed. The heterostructure is a non-Hermitian system that possesses reciprocal and nonreciprocal optical transmission characteristics. With low incident power, linear optical characteristic is observed whereas at high incident power, nonlinear optical characteristics is observed. Under the low incident power there is no nonlinear effect, the forward and backward transmission are reciprocal. With appropriate geometric parameters, for forward propagation two exceptional points where the reflection coefficients equal zero can be obtained simultaneously. With high power incident nonlinear effect becomes significant, leading to reciprocity broken and optical bistability observed. We investigated the behaviours of forward and backward transmission as well as the optical bistability under different incident powers using nonlinear coupled mode theory. There is excellent agreement between the simulation results and theoretical modelling. The theoretical study of proposed heterostructure shows it has several novel optical responses under different incident conditions. The proposed heterostructure is relatively simple to fabricate and therefore can be experimentally verified with ease. These unique optical characteristics allow more possibilities for the design of multifunctional devices.