Wide-band high performance optical modulator based on a stack of graphene and h-BN layers with plasmonic edge mode

Abstract

Modulation depth and its associated loss pose a significant challenge in electro-optical telecommunication systems. Optimal modulators strive to enhance modulation depth while minimizing loss rates. We propose a high-performance electro-optical hybrid plasmonic modulator based on graphene, hexagonal Boron Nitride (h-BN), and Molybdenum Disulfide (MoS₂) layers. The substrate of the proposed modulator is SiO₂ on a Silicon wafer, where Ag layers are embedded in the SiO₂ layer and on top of the structure. Graphene layers at the edge of the upper and lower Ag layers and h-BN in between them create a waveguide capable of transmitting input light through the structure. Graphene and MoS₂ layers increase the amount of light interaction increasing, in turn, modulation depth. The edge mode in the graphene layers confines light properly and increases the electrical field intensity in a narrow gap. The modulator’s performance is examined using a three-dimensional finite-difference time-domain (FDTD) method. The structure’s modulation depth, for a range of temperature, ranges between 40.54 dB/μm and 42.05 dB/μm. The maximum loss is estimated to be 5.723 dB/μm at 1.3 μm for 0.65 eV chemical potential, which yields a figure of merit (FoM) of 12.5 and extinction ratio (ER) of 99.51 dB. The equivalent circuit for the modulator is investigated in terms of parameters such as energy consumption and modulation bandwidth. The modulator demonstrates an impressively low energy consumption per bit, underscoring its efficiency and practicality. The modulator’s characteristics primarily arise from utilizing a thin layer of h-BN instead of thick dielectric layers. Unlike the previously examined configurations, applying voltage through the graphene layers substantially diminishes the insertion loss.