Monolayer graphene on submicron LiNbO3 thin film waveguide: Carrier properties and their effect on waveguide transmission

Photonic devices are currently advancing towards high integration and miniaturization, necessitating the utilization of low-dimensional materials as pivotal components for the next generation of optoelectronic modulators. In this work, we conduct an in-depth exploration of the waveguide properties of submicron ferroelectric material LiNbO3 when integrated with graphene, utilizing a prism-coupled total reflection system. Our experimental findings underscore the significant enhancements in effective index and coupling efficiency upon graphene coverage, and the calculations exhibit the accumulate of electrons in graphene surface. Such distribution of charge and the spontaneous polarization of LiNbO3 itself not only endows graphene with n-type doping characteristics, but also optimizes the overall waveguide performance. Concurrently, the waveguide transmission stability under visible light is verified. The pronounced modifications in effective index and coupling efficiency demonstrate the feasibility of graphene as an electrode, thereby laying the foundation for future investigations into high-speed optical modulators based on the graphene-LiNbO3 platform.