Experimental And Theoretical Studies On Different Characteristic Solitons Of Passively Mode-locked Fiber Lasers

Passively mode-locked fiber lasers are currently being developed for applications in the science research and industrial production,such as optical fiber communication,sensing,and laser processing.As a low cost and ultrashort pulse source,passively mode-locked fiber laser has the advantages of simple structure,easy alignment and flexible design.In this thesis,different characteristic solitons of the passively mode-locked fiber lasers are experimently and theoretically investigated.By means of accurate dispersion and nonlinearity management,multi-wavelength mode-locked fiber laser,wavelength tunable mode-locked fiber laser,vector soliton mode-locked fiber laser,and bound state soliton mode-locked fiber laser are achieved.The research content of this dissertation is as follows:1.Dual wavelength erbium-doped fiber lasers with a nonlinear polarization rotation and graphene mode locking are studied.The formation mechanism and the interaction of the dual-wavelength conventional solitons in fiber lasers are analyzed by experimental results and numerical simulation.Using chirped fiber Bragg grating technology,the three wavelength soliton sources independently output are realized.The center wavelengths are 1539.5,1549.5 and 1559.5 nm,respectively.The pulse widths are 6.3,5.2 and 4.8 ps,respectively.The spectral bandwidths are 0.42,0.65 and 0.53 nm,respectively.2.A stable dual-wavelength erbium-doped fiber laser mode-locked by nonlinear optical loop mirror in normal dispersion regime is experimentally studied.The formation mechanism of the dual-wavelength dissipative solitons is analyzed.Different from the anomolous dispersion regime,the dissipative soliton has a steep spectral edge.The polarization characteristics of the dual-wavelength dissipative solitons are studied.The two groups of the mode-locking pulses have the same polarization state.Research results show that the dual-wavelength dissipative solitons formed mainly from birefringence-induced filtering effect.3.Wavelength tunable erbium-doped fiber lasers with nonlinear polarization rotation mode locking are proposed.The formation mechanism of the tunable solitons is analyzed in detail.In the anomalous dispersion regime,conventional soliton with the central wavelength in 1560 nm?1575 nm continuous tuning is realized.In the normal dispersion regime,dissipative soliton with the central wavelength in 1560 nm?1592 nm continuous tuning is achieved,the tuning range can be up to 32 nm.When the center wavelength is 1560 nm,the signal to noise ratio is 80 dB,the spectral bandwidth is 9.76 nm,the pulse width is 9.5 ps,and the pulse can be compressed to 500 fs after a section of single mode fiber.The peak power of the compressed pulse is 1 kW.4.An erbium-doped fiber laser to implement vector soliton and scalar soliton mode-locked by single wall carbon nanotubes saturable absorber is proposed.In a near zero dispersion regime,group-velocity-locked vector soliton is achieved and the formation mechanism of the group-velocity-locked vector soliton is numerically simulated.The center wavelength of the pulse is 1560 nm,the pulse width is 500 fs,and the spectral bandwidth is 8.5 nm.The vector soliton is smoothed with a Gaussian type spectral profile.Scalar dissipative soliton is obtained in a normal-dispersion regime.The center wavelength of the pulse is 1563 nm,spectral bandwidth is 12 nm,the pulse width is 13 ps,and the pulse can be compressed to 320 fs after a section of single mode fiber.5.We investigate the generation,interaction,and propagation of bound state solitons in passively mode-locked erbium-doped fiber lasers.Bound state conventional solitons with the phase difference of ? are obtained.The propagation of bound state solitons is experimentally observed and theoretically calculated.Based on single wall carbon nanotubes saturable absorber,a dissipative soliton with a bandwidth of 35 nm and a pulse width of 3.4 ps is obtained,which is compressed to 156 fs.The split and the interaction process of dissipative solitons are studied.The pulse duration of bound state dissipative solitons is estimated as 3.6 ps and the pulse-pulse separation is 30 ps.By exploiting nonlinear amplifying loop mirror technique,bound state of three dissipative solitons is obtained.The modulation depth is 12 dB,the pulse separation is7 ps,and the pulse width is 460 fs.The results show that the formation of bound state solitons is derived from the direct interaction of solitons.