Quantum Engineering Enables Broadband and Robust Terahertz Surface Plasmon-Polaritons Coupler

The in-plane terahertz (THz) surface plasmon polaritons (SPPs) coupler is a key element of THz information transmission and processing. However, existing parallel coupler based on two SPPs waveguides is not robust against perturbations of geometric parameters (arising due to fabrication imperfections) and are limited by the single frequency of operation. In this work, we propose a robust and broadband integrated THz coupler based on the in-plane SPPs waveguides, conducted with the quantum engineering - Stimulated Raman Adiabatic Passage (STIRAP). Our coupler consists of two asymmetric specific curved corrugated metallic structures working as the input and output SPPs waveguides, and one straight corrugated metallic structure functioning as the middle SPPs waveguide. From the theoretical and simulated results, we demonstrate that the SPPs can be efficiently transferred from the input to the output waveguides. Our device is robust against the perturbations of geometric parameters, and meanwhile it manifests broadband performance (from 0.5 THz to 0.8 THz) with a high transmission rate over 70{\%}. This work represents a step forward for significant improvements in THz sensing, THz imaging, on-chip THz signal processing, and other next-generation THz photonic device.