Research On Multi-wavelength Square Pulses From A Ytterbium Doped Fiber Laser

All-normal dispersion mode-locked fiber lasers have been raised concern for their distinctive merits and complex soliton features,and it has a wide range of applications in industry and basic research.There are many ways to realize passive mode locking in ytterbium-doped fiber lasers(YDFL),such as nonlinear polarization rotation(NPR)technology and nanomaterials(graphene,TI,etc).NPR is widely used in high-energy fiber lasers for its high damage threshold.By means of these mode-locking methods,many types of mode-locked pulses are generated from the fiber lasers,such as conventional soliton,dissipative soliton,noise-like pulse,etc.Among them,dissipative soliton resonances(DSR)with square pulse profile attract considerable attention due to their high energy and high coherence.At present,the research on DSR pulses is mainly focused on single wavelength,but the performance of multiple numbers wavelength fiber lasers is more better in some applications.Then the research on multi-wavelength square pulses from a YDFL is of great significance.The mainly details of these include the following sides:1.The history of laser technology is described.Then the study evolvement of multi-wavelength fiber laser and square-wave fiber laser is analyzed.2.The mode-locking theorie of fiber laser is researched.The basic mode-locking theories of NPR are studied,and the pulse transmission equations are constructed.The output characteristics of pulse are simulated by Matlab.3.Wavelength switchable and tunable fiber laser is studied.The YDFL was built up,and abundant mode-locked phenomenon were obtained.The laser achieves switchable mode-locked operation at 1042.8 nm to 1050.2 nm and 1040.9 nm to1048.1 nm,as well as tunable operation at 1042.77 nm to 1045.33 nm.The research findings offer experimental guidance for the research of wavelength switchable and tunable fiber laser.4.The DSR square wave YDFL is studied.For further research,the laser is obtained in the two groups of high-energy square pulse broadening.The pulse widths are 37.7 ns and 10.5 ns,respectively,which energy is 152.7 n J.The reason of multi-wavelength lasing can be analyzed by measuring the wavelength interval of output spectrum of continuous wave.It is helpful to deepen the understanding of the output characteristics of multi-wavelength square wave fiber lasers.5.The multi-wavelength YDFL with SRS is researched.Dual-wavelength mode locking is realized which is caused by SRS in the experiment.The tunable range of dual-wavelength spectrum can be 11.7 nm by adjusting PC.Under the pump power of375 m W power the operation of triple-wavelength mode locking is activated,three peak are located at 1022.8 nm and 1073.4 nm and 1120.7 nm,the distance between the two peaks of about 50 nm,comprehend the triple-wavelength formation course and the structure of the pulse.The results contribute to understanding multi-order Stokes waves and SRS in fiber lasers.