Graphene-assisted dual-frequency third harmonic generation in nonlinear metamaterials for high-efficiency on-chip terahertz integration

Nonlinear effects in the terahertz regime play a pivotal role in advancing terahertz wave generators with higher frequencies, particularly through harmonic generation processes. However, the development of efficient nonlinear terahertz materials that exhibit high conversion efficiency, compatibility with large-scale on-chip integration, and stable operation at room temperature remains a significant challenge. Graphene-assisted nonlinear metamaterials provide a promising platform for investigating nonlinear effects within the terahertz frequency regime. In this study, we present a transmission-mode nonlinear metamaterial-integrated device that synergistically combines the resonant characteristics of metamaterials with the nonlinear enhancement properties of graphene. This integrated structure enables efficient dual-frequency third harmonic generation (THG) at 9.535 THz and 10.959 THz, achieving a conversion efficiency of 0.127% under a pump intensity of 1 MW/cm2. A comprehensive theoretical analysis is conducted to investigate both the linear and nonlinear operational characteristics of the integrated device. The enhancement mechanism of THG is systematically investigated by examining the electric field distributions and plasmonic resonance characteristics. Additionally, the influences of device structural parameters and terahertz wave incidence angle on the operational characteristics are thoroughly evaluated. The proposed graphene-based nonlinear metamaterial shows exceptional potential for broad applications in terahertz integrated systems and related photonic technologies.