Nonlinear Graphene Hybrid Plasmonic Waveguide for Enhanced Kerr Effect and Compact Optical Devices

Abstract

Enhancing the nonlinear Kerr effect in plasmonic waveguides remains challenging due to limited light confinement and weak nonlinear responses of conventional materials. In this work, we hypothesize that embedding a graphene monolayer between nonlinear DDMEBT layers can substantially strengthen the Kerr nonlinearity and reduce the device footprint. To verify this hypothesis, we design a nonlinear graphene hybrid plasmonic waveguide (NGHPW) composed of a thin silver cap, two DDMEBT (2-[4-(dimethylamino)phenyl]-3-[4-(dimethylamino)phenyl]ethynylbutadiene-1,1,4,4-tetracarbonitrile) layers, and a graphene monolayer on a silicon-on-insulator (SOI) platform. Finite element method (FEM) simulations using COMSOL Multiphysics are employed to analyze the influence of geometric parameters on effective mode index, propagation length, effective mode area, and threshold power. Our findings demonstrate a high nonlinear coefficient of 3.99 × 10⁸ W⁻¹km⁻¹ (γ = 3.99 × 10⁸ W⁻¹km⁻¹), a minimum effective mode area of 0.032 μm² (Aeff = 0.032 μm2), and Kerr nonlinear figure of merit of 0.02 (FoM = 0.02). The NGHPW exhibits superior performance for small nonlinear layer thicknesses (hnl < 15 nm), resulting in stronger field localization and improved nonlinear interaction. As a practical application, a directional coupler based on the proposed structure achieves an ultra-short coupling length of 2.5 μm for a 100 nm separation. These results confirm the potential of NGHPW as a compact, tunable, and highly efficient platform for integrated nonlinear photonic devices.