Ultra-small shape-simplified optical diode derived from topology optimal design in plasmonic waveguide

Abstract

We present in this paper an ultra-small plasmonic optical diode, which converts a symmetric mode into an asymmetric one and reflects backward propagation of the symmetric one, with a metal-insulator-metal (MIM) structure. A profile of an optical diode is derived from a topology optimal structure obtained in our previous study, and it is simplified so as to reduce insertion loss and difficulty in fabrication. An optimal profile is found out using a differential evolution (DE) which is one of the evolutionary algorithms, and optimization is carried out taken into account fabrication tolerance. According to the results of numerical simulation by 2D finite element method (FEM), the optimized plasmonic optical diode has insertion loss of <0.5 dB, reflection of <−20 dB in the forward propagation, and backward transmission of <−20 dB over C-band, and it is tolerant of ±5 nm boundary deviation. In addition, this device has an extremely small functional region (<1.5 µm).