Graphene-based valley photonic crystal waveguides for hot electron-assisted electro-absorption modulations

Owning to the remarkable optical and electrical properties of graphene, its integration with Si waveguides allows for the achievements of ultracompact structure, high modulation efficiency, and large operation bandwidth, which is promising for the applications in on-chip optical interconnects. However, the manipulation of robust optical signals using 2D materials remains underexplored, and thus, it is a great challenge for realizing graphene-based topological photonic circuits. In this paper, we experimentally demonstrate an electrically controllable valley-Hall device by transferring a single-layer graphene onto the valley photonic crystal waveguide. Through modifying the Fermi level of graphene with current-induced hot electrons, we realize the electrical modulation of valley-locked light waves based on electro-absorption effect, operating at the near-infrared regime of 184–194 THz. The modulation depth of nearly −0.08 dB/um is obtained with an active waveguide length of merely 25 μm. Moreover, the simulated optical responses of the device under the transient electrical modulations exhibit rise and fall times of 5.1 and 1.9s6 ns, respectively. This graphene-based hot electron modulation mechanism, with the integration of Si-based valley photonic crystals across a broad range of telecom wavelengths, supplies a novel scheme for the on-chip active topological photonic devices.