Researches On The Regulation Of Soliton Parameters In Passively Mode-locked Fiber Laser

Ultrashort pulses have many applications in industry,armament and medicine,for example,laser processing,surgery,supercontinuum generation,optical imaging and terahertz-wave generation.Due to the compact cavity,affordability,stable operation,and the ability of generating ultrashort pulses with high beam quality,passively mode-locked fiber lasers have been widely applied in those fields.In this paper,we have investigated and analysed the regulation of soliton parameters in passively mode-locked fiber lasers.By adjusting the structure and parameters of passively mode-locked fiber lasers,the regulation of soliton types,pulse width,central wavelength,and solitons separation have been realized.The main contents of this article are as follows:1.The generation of conventional solitons,stretched pulses and disspative solitons in 1.55-μm and 2-μm region have been respectively realized,and a fiber laser that can deliver conventional solitons or stretched pulses has been demonstrated.Firstly,by building single-wall carbon nanotubes(SWNTs)mode-locked erbium-and thulium-doped fiber lasers with the negative,near-zero and normal dispersion,we have obtained three types of solitons in 1.55-μm and 2-μm region.Additonaly,we have proposed a fiber laser with the net cavity dispersion of negative and near-zero.A fitering effect based on the nonlinear polarization rotation is induced in the fiber laser.The bandwidth of the filter can be varied by roating and twisting the polarization controller(PC)in the cavity,which in turn changes the stretching factor of soliton.While the stretching factor is large enough,the fiber laser can deliver stretched pulses;conventional solitons are obtained as the stretching factor is small enough.2.The regulation of soliton pulse width has been realized by managing the cavity dispersion,and a fiber laser that can deliver two kinds of pulses with the pulse width ratio of~20 has been demonstrated.Firstly,the cavity dispersion of the SWNTs mode-locked fiber laser is managed by reducing the single-mode fiber in the cavity,and solitons with different pulse widths have been obtained.Secondly,a fiber laser that can simultaneously emit two kinds of pulses has been proposed.The two kinds of pulses propagate along two different paths in the cavity,whose dispersion are?2.23 ps~2 and?0.259 ps~2,respectively.Correspondingly,the pulse widths of the two kinds of pulses differ great with each other,which are 19.4 ps and 1.2 ps,respectively.3.Taking advantages of the birefringent filtering effect,we have proposed a black phosphorous(BP)mode-locked erbium-doped fiber laser with the wavelength tuning range of 63 nm and a SWNT mode-locked thulium-doped fiber laser with the wavelength tuning range of 32 nm.On the one hand,in the BP mode-locked fiber laser,the central wavelength of the delivered solitons can be flexiblely tuned from 1529 nm to 1592 nm by adjusting the PC.On the other hand,in the SWNT mode-locked thulium-doped fiber laser,the wavelength is tuned in a range of 1892 nm to 1924 nm,and two kinds of dual-wavelength mode locking operation can also be achieved by increasing pump power and rotating the PC in the cavity.We have obtained various kinds of bound solitons with the locked separation of .7 ps in a passively mode locked erbium-doped fiber laser by inducing a abry-Perot(F-P)microcavity.The intensity ratio of the soliton within the bound oliton can be continuously tuned by adjusting the PC.The formation dynamics of the acheived bound soliton reveals that the fiber laser directly evlves into bound state from continuous wave without experiencing single-soliton mode-locking process.Numerical results match well with the experimental observation and further confirm that the generation of bound solitons with locked separation is attributed to the F-P microcavity.