Two-dimensional Material Saturable Absorber Passively Mode-locked Fiber Lasers

Ultrashort pulse laser has important applications in material processing,optical communication,medical treatment and ranging due to its high peak power,high pulse energy and short duration.Passive mode-locked fiber laser has become a common technology of ultra-short pulse light source because of its simple structure,few discrete devices and good system stability.Saturable absorber mode-locking technology is a common method for passively mode-locked fiber lasers.Two-dimensional nano-material saturable absorber has become one of the current research hotspots due to its simple preparation,low cost and wide operating band.This thesis is based on the application of two-dimensional nanomaterials in mode-locked fiber lasers,and conduct theoretical and experimental studies.Using single-walled carbon nanotubes,graphene oxide and tungsten disulfide as research objects,mode-locked pulse output were obtained experimentally in fiber lasers,and its characteristics are studied.The content of this paper mainly includes1.The research status of saturable absorber mode-locked fiber lasers is investigated.The preparation of new two-dimensional nanomaterials and the measurement methods of saturable absorption properties are introduced in detail.The method of inserting saturable absorber into laser is summarized.2.The basic principle of mode-locking technology is expounded.The working principle of three passively mode-locked fiber lasers and their advantages and disadvantages are described.The types of mode-locked pulses in different dispersion domains of fiber lasers are introduced one by one.3.Carbon nanotubes saturable absorber was fabricated and applied to erbium-doped fiber laser.The conventional soliton pulse output was obtained with a pulse width of 910 fs.By increasing the pump power,the dual-wavelength mode-locked pulse output is obtained.The carbon nanotube was applied to ytterbium-doped fiber lasers,and the dissipative soliton mode-locked output is obtained.The spectral width is 0.7 nm and the pulse width is 600 ps.Graphene oxide saturable absorber was prepared and used in erbium-doped fiber laser to obtain conventional soliton pulse output,and the pulse width is 1.01 ps.4.WS₂ nanosheets dispersions were prepared by liquid phase stripping method and saturable absorbers were prepared by photo-adsorption method.The mode-locked pulse output is obtained in erbium-doped fiber laser.The spectral width is 0.5 nm and the pulse width is 1.43 ns.Few-layer WS₂ and mono-layer WS₂ saturable absorbers were fabricated respectively,and they were applied in one ytterbium-doped fiber laser to obtain Q-switched pulses.The shortest pulse durations are 2.7?s and 748 ns for few-layer WS₂ and mono-layer WS₂ respectively,and the maximum pulse energy is205 nJ and 154.2 nJ.Thanks to the large modulation depth of mono-layer WS₂,the pulse duration of fiber laser with mono-layer WS₂ is narrower and the peak power is higher.