Study On Two-dimensional Material Saturated Absorber Mode-locked Fiber Laser

The mode-locked fiber laser based on saturable absorber has many advantages,such as low pump threshold,wide wavelength range,ultra-fast recovery time,low cost,simple preparation,flexible and compact design,and easy fiber integration compatibility.Therefore,It is not only an important light source in ultra-fast optical soliton communication,but also widely used in all aspects of high-speed optical fiber communication systems.It is expected to replace other optical fiber lasers in the market.In this paper,related theoretical derivation,numerical simulation and experimental research are carried out around the saturable absorber mode-locked fiber laser.In terms of theory,we describe the influence of dispersion effect,nonlinear effect,gain effect and birefringence effect on the output light pulse in the mode-locked fiber laser based on saturable absorber.And further based on Maxwell's equations,the transmission equation of light pulse in single mode fiber-nonlinear Schrodinger equation?NLSE?and the transmission equation of light pulse in gain fiber-Jinzibao equation?GLE?are derived.In terms of numerical simulation,we use the Split-step fourier method?SSF?to solve NLSE and GLE,use Matlab to perform simulation operations,simulate and discuss the output laser pulses and spectra of the saturable absorber mode-locked fiber laser with different parameters.The influence of the laser cavity length,the optical power of pump light and the parameters of saturatble absorber on the output laser pulse and spectrum of mode-locked fiber laser is analyzed.We found that it is useless to increase or decrease blindly the length of the single-mode fiber and the gain fiber in order to obtain an output pulse with a high peak value and a narrow pulse width.The optimum value should be found.But when the pump power is increased and the modulation depth of the SA is increased,a higher power output pulse can be obtained.Although the numerical simulation results are different from the actual experimental results,through numerical simulation,we can get the influence of some parameters on the experimental results in the experimental process,which still have important guiding significance for the experimental work.The above simulation results show that we need to reasonably select the relevant parameters in the laser design process to obtain an optimized mode-locked laser output.In terms of experimental research,for the diversification of two-dimensional materials and mode-locked methods,we conducted experiments on bismuth selenide?Bi₂Se₃?,Molybdenum disulfide?MoS₂?and graphene using three different fabrication schemes to study the output characteristics of different material mode-locked devices and analyze the advantages and disadvantages of various methods.Due to the preparation process,the graphene film mode-locked device produced by the mechanical peeling method did not obtain good results.The use of MoS₂/PVA thin film and Bi₂Se₃taper fiber achieve a good picosecond magnitude soliton locked-mode pulse output.In the process of using the MoS₂/PVA film and Bi₂Se₃ taper fiber as the mode-locked devices,the switching among the bright pulse,the dark pulse and the bright-dark pulse pair,dark pulse mode-locked output with adjustable repetition rate,dark pulse mode-locked output with pulse width tunable,and multi-wavelength mode-locked can be realized by properly adjusting the pump light power and polarization state.These phenomena validate the pulse output diversity of a mode-locked fiber laser that can saturate the absorber.