Research Of Bilayer Graphene For Its Carrier Transport And Passively Q-switch Roled In On Microfiber Evanescent Field

Ultrafasl pulse laser has an important role in communication, medicine, biology and modern national defense. Due to its advantages of structure, stability, heat dissipation and collimation, Q-switched fiber laser is widely used in the realization of the pulse output. Graphene as a new kind of functional material has the ultrafast carrier transport properties and linear dispersion electronic band structure, which makes the graphene have been widely applied as the saturable absorber in the field of Q-switched fiber laser. However, due to the low damage threshold of the graphene material, it makes the Q-switched fiber laser cannot afford the high-power laser system. Based on the above discussion, in this paper, we use the graphene-microfiber composite waveguide as a new saturable absorber, and achieve the stable Q-switched output at a high pump power with this saturable absorber.Firstly, we synthesized the bilayer graphene film on Cu foils by a home-built chemical vapor deposition (APCVD). We explored the carrier transport properties of the bilayer graphene in the temperature range of 0 ? to 240 ? (273 K-513 K) and analyzed the experimental results. The temperature dependence of the carrier density is successfully simulated by the thermal activation (TA) model, and the experimental phenomenon of the carrier mobility does not change with temperature also is explained by the theory.Secondly, we prepared the taper-microfiber with fused biconical taper method (the diameter of the microfiber is from 4 um to 10 ?m). BeamPROP module of the Rsoft software is used to simulate the radial mode field distribution of taper waist region of the microfiber with different diameter. The simulation results show that with the decrease of the diameter (taper waist region), the radial mode field diameter increases in relation to the diameter of taper waist region. Well, the intensity of the evanescent wave is bigger and the light transmission efficiency (?) is more and more small.Finally, we use the graphene-microfiber composite waveguide as a new saturable absorber, and achieve the stable Q-switched output from 220 mW to 600 mW. We also have a detailed discussion of the pump power from 300 mW to 500 mW. Experimental results show that the pulse width decreased from 4.11 us to 2.06 us and the repetition frequency increased from 50.38 kHz to 73.06 kHz.