Experimental Research Of Q-switched And Mode-locked Fiber Laser Based On PbS?MXene

Due to the advantages of good beam quality,low cost,compact structure and high conversion efficiency,fiber laser has been widely used in precision machining,biological microscope,medical surgical equipment,optical fiber communication and lidar.In fiber lasers,loss element in fiber laser is the key factor to realize Q-switching and mode-locking.In recent years,the emergence of new optical saturation absorbers has promoted the development of fiber lasers.Compared with the traditional method using active modulator method,the new 2D materials have attracted researchers'interest and attention due to their characteristics of wavelength independence,high heat dissipation and high damage threshold.This paper mainly focuses on the application of lead sulfide(PbS)and Ti₃C₂T_xMXene saturable absorbers in short-pulse lasers.The research can be summarized as follows:1.In the experiment,a passively Q-switched fiber laser with PbS-microfiber saturable absorber was constructed.The PbS dispersion was prepared by liquid-phase stripping method.PbS was combined with the microfiber by optical deposition method to form a saturable absorption device.A dual detection system was used to perform a nonlinear test on PbS.The saturation intensity and the modulation depth were 3 MW/cm²and 30.9%.The aturable absorber was welded into the resonant cavity,and a stable Q-switched pulse was obtained within the pump power range of 30-220 mW.The repetition frequency of the Q-switched pulse ranges from 17.21-71.72 k Hz,and the minmun pulse duration was 2.74?s,the maximum pulse energy was 53.24 n J.2.Passive mode-locked fiber lasers based on Ti₃C₂T_x MXene with polyvinyl alcohol(PVA)composite film saturable absorber were built at 1.5?m and 1.0?m,respectively.The non-linear absorption characteristics of the Ti₃C₂T_x MXene composite film were measured,and the light saturation intensity was 2 MW/cm²,and the modulation depth was 3.6%.The Ti₃C₂T_x MXene composite film was applied to the Erbium-doped fiber laser to obtain a stable traditional soliton mode-locked pulse with repetition frequency of 11.1 MHz,the center wavelength of 1573.2 nm,the spectrum full width at half maximum of 2.7 nm,and the pulse duration of 1.73 ps.Constantly increasing the pump power to achieve the 56th harmonic mode-locked,the maximum repetition frequency was 622.2 MHz,and the pulse duration was 1.31 ps.By changing the polarization state,a dual-wavelength pulse output with harmonic mode-locked and fundamental frequency mode-locked was also observed.The center wavelengths were 1575.6 nm and 1587.5 nm,and the full width at half maximum was 3.1 nm and 3.4 nm,respectively.The Ti₃C₂T_x MXene composite film was applied to a Yb-doped fiber laser,a stable mode-locked pulse with the repetition frequency of 11.8 MHz and the pulse duration of 13.33 ps was achieved at 1072.85 nm.3.Constructed 1.0?m and 1.5?m synchronous dual-wavelength fiber lasers.The two ring resonators share a common branch containing a graphene saturable absorber.Based on the saturable absorption and cross-phase modulation effect,the synchronous dual-wavelength mode-locked was realized.Without losing synchronization,the measured maximum cavity mismatch was 0.8 mm.Within this mismatch range,the frequency change value of the Yb-doped cavity and the Er-doped cavity was 0.76 k Hz.