Two-dimensional Composite Material And Equivalent Saturable Absorber Study On Erbium-doped Fiber Laser Mode-Locking

Fiber lasers have been widely used in optical communication system,spectral analysis,laser processing,laser medical treatment,biopharmaceuticals,and material processing and so on due to their good mechanical properties,high beam quality,small size,and easy thermal management.Data communication system increasingly uses fiber communication system as the transmission path for information,and the central wavelength of output pulses of erbium-doped fiber laser is around 1.55μm,which includes most of the working bands required for fiber communication.Therefore,the research on erbium-doped fiber laser is of great significance.The mode-locked technology of output pulses in erbium-doped fiber laser has been widely studied,including two-dimensional new material saturable absorbers and nonlinear optical loop mirror（NOLM）,nonlinear polarization rotation（NPR）and nonlinear amplifing loop mirror（NALM）–like saturable absorbers mode-locked techniques.It becomes quite important to explore the effect of different mode-locked techniques on pulse generation.In this paper,based on WS₂/MoS₂ composite saturable absorbers and NPR hybrid mode-locked technology,NOLM mode-locked technology,the traditional soliton characteristics of erbium-doped fiber laser output are studied.The main contents of this paper are as follows:1.The WS₂/MoS₂ composite materil film was made by the liquid phase exfoliation method,and the composite material saturable absorbers was made by transferring the composite material film to the stretched area of the stretched optical fiber,and its saturable absorption characteristics were tested.2.Based on NPR mode-locked technology,the hybrid mode-locked erbium-doped fiber laser was constructed by using polarization-dependent isolators,polarization controllers,and preparative composite saturable material absorbers and other optical devices.In the experiment,the pump power gradually increases to reach the mode-locked threshold,and the polarization state was adjusted to achieve a stable mode-locked state.The central wavelength of the laser output is 1572.28 nm,the repetition frequency of the pulse is 20.6MHz,the 3 d B bandwidth of the spectrum is 7.8 nm,and its signal-to-noise ratio is a conventional soliton of 69 d B.The polarization state in the cavity is tuned by PC,and the central wavelength is shifted between 1566.98 nm and 1572.28 nm,and the tuning range is about 5.3 nm.3.The stretched fiber in the above-mentioned laser resonator is looped,and the composite material film is covered in the stretched area to obtain the saturable absorber,which is connected to the fiber laser again.The pump power is increased to 200 m W and the PC is slowly adjusted to obtain stable Q-switched mode-locked pulses,the central wavelength of the output pulse spectrum is 1561.01 nm.In the experiment,the pump power was adjusted to obtain the repetition frequency and pulse duration of the Q-switched mode-locked pulse with different pump powers.4.A passively mode-locked erbium-doped fiber laser was constructed based on NOLM technology,the PC was adjusted and the pump power is increased to 270 m W to achieve a stable mode-locked state.The output central wavelength,spectral width,repetition frequency and signal-to-noise ratio is 1557 nm,4.2 nm,21.01 MHz and 68 d B of traditional soliton pulses,respectively.With increasing pump power,a tuning range of 1.5 nm was obtained at the central wavelength.The output of loosely bound state soliton pulses was obtained by adjusting PC when the pump power is increased to 360 m W.