Prepararation,Characterisation And Application Research Of Two-Dimensional Layered Saturable Absorber In Pulsed Fiber Laser

Pulsed fiber lasers,due to its small size,strong heat dissipation,high beam quality,high stability,pulse fiber laser conversion efficiency,have been widely used in optical fiber communication,laser processing,industrial manufacturing,national defense,biomedicines,fiber sensing,lidar and nonlinear optics.At present,the pulse output in the optical fiber laser is mainly obtained by Q-switched and mode-locked,and it is a simple and widely used method to realize passively Q-switched and mode-locked by using saturable absorber（SA）.In recent years,with the emergence of graphene,various new types of two-dimensional layered materials are widely used in optical fiber lasers due to their excellent saturated absorption properties.However,most two-dimensional material SAs have different applications in pulsed fiber lasers and have their own limitations.Therefore,it is particularly critical to improve the performance parameters of SA in order to improve the output index of the laser.This thesis presents an experimental improvement study in terms of material preparation methods,design of cavity structures and selection of new materials.The preparation and characterisation of two-dimensional layered saturable absorbers such as bismuth（Bi）,bismuth telluride（Bi₂Te₃）and ternary topological insulator bismuth selenide telluride（Bi₂Se₂Te）and their application in erbium-doped fiber lasers are presented in detail.The main research contents of this thesis are as follows:（1）Bi single-element saturable absorbers were successfully prepared by liquid-phase exfoliation method,and their nonlinear optical properties were tested experimentally.Later,it was used in erbium-doped fiber laser,and the traditional soliton with output center wavelength of1569.25 nm,fundamental frequency of 4.3 MHz,pulse width of 1.09 ps and stable Q-switched pulse with the repetition frequency from 36.40 k Hz to 62.80 k Hz were finally obtained.The experiments show that Bi has excellent nonlinear saturable absorption properties and has the potential to become a high-performance optoelectronic device material.（2）High-energy erbium-doped passive fiber laser was built based on the CVD-Bi₂Te₃saturation absorber.High-quality Bi₂Te₃nanofilms were prepared and characterized by CVD,and the nonlinear saturable absorption characteristics of Bi₂Te₃were measured,which was made into saturable absorber in erbium-doped fiber laser.A stable mode-locked pulses were successfully obtained with a central wavelength of the output spectrum at 1558.42 nm,a 3-d B bandwidth of 1.86 nm,a maximum output power of 40.74 m W and a maximum single pulse energy of 23.9 n J（the highest single pulse energy value）.The laser damage threshold was up to33 m J/cm².The experimental results show that the Bi₂Te₃SA prepared by CVD method has excellent nonlinear saturable absorption characteristics,which can achieve the pulse output of large energy in the field of ultrafast optics,and this experiment also provides a new way to obtain the novel SA with high damage threshold.（3）The ternary topological insulator Bi₂Se₂Te was successfully prepared by liquid-phase exfoliation and was tested for its nonlinear optical properties.The modulation depth and saturation intensity were measured to be 4.76%,6.23 MW/cm²,respectively.Bi₂Se₂Te was used as saturation absorber in erbium-doped fiber laser,the conventional mode-locked soliton with the central wavelength of 1559.50 nm,fundamental frequency of 4.32 MHz and theoretical narrowest pulse width of 755 fs was obtained by changing the proportion of different polymers of SA.The application of Bi₂Se₂Te in 1.5μm band fiber laser is confirmed,and provides new guidance for exploring the development of new materials as the next generation of material devices.