Research On High Repetition Frequency Fiber Laser Based On New Photonic Devices

Because of its narrow pulse width,high peak power,good beam quality,high conversion efficiency,good heat dissipation and compact structure,pulsed fiber laser is widely used in material processing,biomedical,optical communication,scientific research,military system,remote sensing detection and other fields.As we all know,it is undoubtedly one of the best ways to make new two-dimensional materials into saturable absorber devices for ultrashort pulse laser generation.In particular,the pulse repetition rate of the pulsed fiber laser based on two-dimensional materials is usually lower than 1 GHz,and the high repetition rate pulsed fiber laser can be widely used in optical frequency comb,optical communication,nonlinear optical biological imaging and so on because of its unique beam characteristics.Therefore,it is of great significance to further study the high repetition rate pulsed fiber laser based on twodimensional materials.Two dimensional materials have attracted much attention due to their rich elements,environmental friendliness and excellent photoelectric properties.In particular,twodimensional materials have excellent nonlinear optical properties such as large nonlinear refractive index,fast response,large nonlinear polarizability and wide band saturated absorption,which make them have broad application prospects in saturable absorbers,wavelength converters and optical limiters.Therefore,it is of great significance to further explore the nonlinear optical properties of two-dimensional materials.Some traditional two-dimensional materials,such as graphene,black phosphorus(BP),graphdiyne(GD),MXene,bismuthene and transition metal dichalcogenides(TMDs),have been widely studied as saturable absorbers to realize ultrashort pulse laser.These traditional two-dimensional materials show some outstanding properties,but there are also some inherent shortcomings.At present,the MXene layer is thick and the yield of single or few layers is very low.Therefore,more effective preparation or separation methods are needed to obtain MXene materials with different layers and properties.The stripped BP is easily oxidized when exposed to air and water.Therefore,to find and explore new two-dimensional materials has become an urgent problem.In this paper,we mainly study the preparation,nonlinear optical properties of MXene Ti3C2Tx,SnS and Ag2S,and their application in fiber laser to realize high repetition rate ultrashort pulse.We have measured their nonlinear optical properties by using a double balance detection system.MXenes is prepared by selecting the A layer of MAX phase etching layered ternary carbides.The reason why we call this material MXene is that it is similar to two-dimensional graphene.Its general formula is Mn+1XnTx.M is an early transition metal(Zr,Mo,Ti,Nb,V,Ta).X is expressed as C,N and CN.Tx represents a variety of surface functional groups(-OH,-O,and-F).Finally,the saturation absorption characteristics of MXene Ti3C2Tx nanofilms with modulation depth of 0.96%and low saturation light intensity of 256.9 MW cm-2 are explained.Based on two-dimensional MXene Ti3C2Tx saturable absorber,harmonic mode locking with repetition rate of 218.4 MHz was realized.SnS,a mysterious twodimensional semiconductor material,has attracted extensive attention due to its outstanding optical,electrical and optoelectronic properties.Its optical absorption coefficient can reach 104 cm-1.Finally,the saturation absorption characteristics of SnS nanosheets with modulation depth of 5.8%and low saturation light intensity of 52.2 MW cm-2 are explained.Based on the two-dimensional SnS saturable absorber,105 order harmonic solitons with repetition rate of 459 MHz were realized.Ag2S,as a new flexible and high-performance two-dimensional transition metal sulfide,has high absorption coefficient(?104 cm-1),large magnetoresistance effect and small direct band gap(0.9-1.1 eV),It has attracted great interest due to its extremely low solubility(Ksp=6.3 × 10-50),high chemical stability,low toxicity,optical limiting property,extraordinary metalloid ductility,high plastic deformation strain and unique layered structure.Finally,the saturation absorption characteristics of Ag2S nanosheets with modulation depth of 15.5%and low saturation light intensity of 250.4 MW cm-2 are explained.Based on two-dimensional Ag2S saturable absorber,229 order harmonic solitons with repetition rate of 1.1 GHz were realized.