1.6μm Band Multimode Interference Effect Mode Locking And Supercontinuum Generation

By locking the phase relationship between the longitudinal modes in the laser resonator,ultrashort pulse fiber lasers are playing an increasingly important role in industrial and medical fields.Research on mode-locking methods such as nonlinear polarization rotation,nonlinear optical ring mirrors,and active modulation structures has become mature,and the research of multimode interference effect mode-locked lasers still has a bottleneck that the length of multimode fibers is difficult to accurately control.In addition,the 1.6 μm band laser has potential application value in the field of biomedicine.Therefore,this thesis carried out the research of 1.6 μm band ultrafast fiber laser based on multimode interference effect,and on this basis,the generation of supercontinuum light source was studied.The specific research content is as follows:1.A mode-locked fiber laser based on multimode interference effect was designed,and the evolution of mode-locked pulses in the negative dispersion region and near zero dispersion region was studied.Firstly,a single-mode-graded-index multimode-single-mode(SMS)structure was built in the near-zero dispersion region to realize the output of stretched pulses and dispersion management soliton molecules.The central wavelength of the stretched pulse is 1528 nm,and the pulse width is 973.2 fs.Chirped pulse amplification technology and dispersion compensation compress the pulse width to 280.1 fs.The spectral modulation period of the dispersion management soliton molecule is 0.32 nm,and the pulse width of a single dispersion management soliton molecule is 4.04 ps.On that basis,a piece of step-index multimode fiber(SIMF)was inserted between the graded-index multimode fiber(GIMF)and single mode fiber.Conventional soliton,soliton molecule and noise-like pulse were obtained by the multimode fiber hybrid structure fiber laser.The central wavelength of the conventional soliton is 1601 nm;the central wavelength of the soliton molecule is 1570.5 nm;the central wavelength of noise-like is 1595 nm.2.A hybrid structural fiber laser consisted of SMS and nonlinear polarization rotation(NPR)was constructed to study the output characteristics of its mode-locked pulse.Both wavelength-tunable conventional soliton and noise-like pulse was obtained.The conventional soliton pulse with a central wavelength of 1570.8 nm was output in the negative dispersion region.By tuning the polarization controller(PC),the central wavelength can be tuned from 1588 nm to 1594 nm,and the tunable range is about 6 nm.The noise-like pulse with a central wavelength of 1564.5 nm has a pulse width of 416 fs.3.Research on the generation of supercontinuum based on nonlinear effects was conducted.The traditional soliton pulse and noise-like pulse in the 1.6 μm band were used as seed pulses to pump the highly nonlinear fiber(HNLF)to generate supercontinuum,and the performance of the output supercontinuum was analyzed and compared.The data shows that the supercontinuum stimulated by the noise-like pulse has the widest spectral width,of which the 3 d B width is 337 nm.