Study On Passively Mode-locked Ring Cavity Ultra-fast Soltion Fiber Laser And Its Output Characteristics

Passively mode-locked soliton fiber lasers have the advantages of high conversion efficiency,low cost,compact structure,no need for collimation,and strong adaptability to the working environment,and are widely used in many fields.For example,using them to generate multi-wavelength optical soliton has the advantages of keeping the shape unchanged during transission,which can be used for optical communication,fiber sensing,measurement,metrology and so on.Ultrafast soliton fiber lasers are also ideal tools for studying and generating nonlinear effects.In order to obtain ultrafast soliton fiber lasers that meet different applications,this thesis designs and optimizes ultrafast fiber laser parameters by fabricating saturable absorbers with excellent performance,and conducts in-depth research on mode-locked soliton fiber lasers and ultrafast soliton characteristics,including pulse static characteristics such as bandwidth and working wavelength,as well as nonlinear dynamic characteristics of soliton in dynamic processes such as formation,transmission,and evolution.Finally,the performance of ultrafast fiber lasers can be improved and its output can be controlled,such as femtosecond soliton generation,multi-wavelength mode locking,high repetition rate output,switchable output state and multi-channel output.The main research contents of this thesis are as follows:(1)Research on ultrafast fiber laser and its output characteristics based on Molybdenum disulfide(Mo S2).Mo S2 is deposited on the tapered fiber by magnetron sputtering to prepare a saturable absorber to construct an ultrafast fiber laser and study its output characteristics.The saturable absorption of Mo S2 can be used for laser mode locking,and its high nonlinear effect can be used to generate multi-wavelength,highorder harmonics,and multi-component vector pulses.Based on the dual effects of Mo S2,we not only experimentally achieved dual-wavelength 44 th and 52 nd harmonic mode locking.A new-type three-component bright-dark-bright(BDB)vector pulsed was also discovered.The research ruslts shown that a single BDB pulse can be considered to be composed of orthogonal bright pulse and dark-bright pulse pair.This research is of great significance to multi-component vector fiber lasers.(2)The study of ultrafast soliton fiber laser and its output characteristics based on nonlinear polarization rotation(NPR)was carried out,and the formation mechanism and evolution characteristics of dip-type sidebands were explained.Inspired by the dual effect of Mo S2,a highly nonlinear fiber was inserted into the ultrafast fiber soliton laser,a dual-wavelength fiber laser with adjustable wavelength and switchable dark pulse and bright pulse was designed.During the study of soliton fiber lasers,a dip-type sideband different from the Kelly sideband was observed.Using soliton fiber ring laser modelocked by NPR,the formation and evolution of dip-type spectral sideband were studied numerically and experimentally.A theoretical model that can predict the position of the dip-type sideband is proposed,and it is pointed out that the formation of the dip-type sideband is caused by the local destructive interference effect between the soliton and the dispersive wave.The thesis strictly deduces the expression of the position of the diptype sideband,which shows that the position of the dip-type sideband on the frequency spectrum can change with the pulse width.Experiments and simulations verify the reliability of the dip-type sideband theoretical model,experimental observations and numerical simulations can well confirm the theoretical predictions.(3)A saturable absorber with a symmetric mutation fiber structure(GIMF-SIMFGIMF-SA)is proposed and demonstrated,and an ultrafast soliton fiber laser and its output characteristics based on the symmetric mutation fiber structure are carried out.The fiber laser realizes femtosecond soliton mode-locking operation and repetition rate tuning.The duration of the soliton is 333.72 fs,and the repetition rate can be adjusted from 10.29 MHz to 901 MHz.In order to obtain pulsed fiber lasers that meet the requirements of different applications,numerical simulation and experimental research on the multi-state output of femtosecond fiber lasers based on symmetric mutation fiber are carried out.Fiber lasers can output three different optical pulses,namely conventional soliton,second-order bound state and noise-like pulse.Experimental and simulation results show that the output state of the fiber laser can be switched by adjusting the pump power.(4)An integratable N-ring-cavity ultrafast soliton fiber laser was designed and demonstrated.In order to meet the design requirements of higher laser integration,lower cost and more comprehensive functions,an integratable N-ring-cavity(N is an integer,N=1,2,3,...,n)femtosecond soliton fiber laser based on optical circulators are designed and demonstrated.In order to prove the feasibility of cascaded N-ring-cavity fiber laser,taking the case of N=2 as an example,a cascaded double-ring cavity fiber laser was designed and studied.Experimental results show that each cascaded single ring cavity can work independently,and the pulse widths of the soliton output from cavity 1 and cavity 2 are 358.6 fs and 458.4 fs,respectively.The research of N-ringcavity femtosecond fiber laser is of great significance to the miniaturization,integration and multi-port output of ultrafast fiber lasers.