The Study Of Passively Mode-locked Fiber Laser Based On Graphene/WS2 Nanocomposites

Ultrafast fiber lasers have been widely used in fields of national defense and military,metering statistics,electronic storage,fiber optic communication,biomedicine and material processing due to its advantages,such as high environmental stability,narrow pulse width,high peak power,high electro-optical conversion efficiency,high heat dissipation,high beam quality,small size and easy integration.The ultrafast laser output is usually achieved by passively mode-locked fiber laser based on saturable absorber.The exploration of saturable absorbers with excellent nonlinear absorption properties has important theoretical and practical value for the development of passively mode-locked fiber laser.In recent years,two-dimensional heterostructures and nanocomposites prepared by layer-by-layer stacking or mixing different two-dimensional nanomaterials possess the properties of band alignment and the transport of interlayer charges and excitons,which have become research hotspots in many fields.In this thesis,we have studied the nonlinear optical properties of graphene/WS2 nanocomposites saturable absorber.We have studied the traditional soliton mode-locked erbium-doped fiber laser and single and dual-wavelength switchable dissipative soliton mode-locked ytterbium-doped fiber laser,which both based on graphene/WS2 nanocomposites saturable absorber.The main research contents of this thesis are as follows: 1.The study of erbium-doped passively mode-locked fiber laser based on graphene/WS2 nanocomposites saturable absorber.The graphene/WS2 nanocomposites(G/W)film was fabricated by the liquid phase exfoliation method and vacuum suction filtration.The size and number of G/W nanosheets were characterized by transmission electron microscope(TEM).The thickness,composition,material crystallinity,and bonding mode of the G/W film were characterized by atomic force microscope(AFM),Raman spectroscopy,X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and UV-Visible spectrophotometer(UV-Vis),respectively.The characterization results indicate that G/W was successfully fabricated.The effect of charge transfer at the G/W interface on its nonlinear absorption properties was studied based on the first-principles calculations.The G/W saturable absorber(G/W-SA)was fabricated by transferring the G/W film to the microfiber.The nonlinear optical properties of G/W-SA were measured by P-scan technology,which shows that the modulation depth of G/W-SA is higher than that of Graphene saturable absorber and WS2 saturable absorber.The research of traditional soliton mode-locked erbium-doped fiber laser based on G/W-SA was carried out.The G/W-SA was inserted into the erbium-doped fiber ring cavity.By adjusting the pump power and polarization controller,the traditional soliton with the central wavelength of 1565 nm,the 3-d B bandwidth of 4.4 nm,the repetition frequency of 17.39 MHz and the signal-to-noise ratio of 60 d B was obtained.2.The study of single and dual-wavelength switchable passively mode-locked ytterbium-doped fiber laser based on graphene/WS2 nanocomposites saturable absorber.The generation mechanism of multi-wavelength mode-locked pulses is summarized.We have prepared the G/W-SA suitable for ytterbium-doped fiber laser and measured the nonlinear optical characteristics of G/W-SA.The experimental study was conducted based on G/W-SA single and dual wavelength selectable ytterbium dissipative soliton mode-locked fiber lasers.The G/W-SA was inserted into the ytterbium-doped fiber ring cavity.By adjusting the pump power,a stable single-wavelength mode-locked pulse with the central wavelength of 1066.2 nm,the repetition frequency of 19.68 MHz,the 3-d B bandwidth of 2.1 nm,the pulse width of 450 ps and the signal-to-noise ratio of 65 d B was obtained.By adjusting the polarization controller,we have observed that the single-wavelength dissipative soliton became the dual-wavelength dissipative soliton.The central wavelengths of the dual wavelengths dissipative soliton are 1066.4 nm and 1069.2 nm,respectively.The corresponding repetition frequencies are 19.684838 MHz and 19.683569 MHz with the signal-to-noise ratio of 52 dB.