Controllable Growth of Graphene Photonic Crystal Fibers with Tunable Optical Nonlinearity

The graphene photonic crystal fiber (Gr-PCF), with graphene coated onto the inner hole walls of the fiber, has shown its superiority in various photonic and optoelectronic applications ranging from electro-optic modulators to environmental sensors. However, these applications mainly utilize the linear optical properties of graphene, and its potentials in the nonlinear optical regime are still waiting to be explored. As for the nonlinear applications, the structure and property of Gr-PCF must be precisely manipulated for the tradeoff between nonlinear enhancement and linear absorption loss of graphene. Here, we propose a pressure-controllable chemical vapor deposition strategy to precisely control the uniform fiber length and graphene thickness, realizing the strong and tunable optical nonlinearity of Gr-PCF with acceptable optical loss. Based on the as-fabricated fiber, the nonlinear harmonic generations exhibit nearly one order of magnitude enhancement compared with those of graphene on planar quartz. Moreover, an ultrafast all-fiber laser employing the nonlinear Gr-PCF as a saturable absorber is demonstrated with similar to 8 mW output power, similar to 2 ps pulse width, and similar to 37 MHz repetition frequency. Our results can technically open up an infusive way to precisely engineer the nonlinear properties of graphene optical fibers and broaden their applications in all-fiber photonic and optoelectronic devices.