Research On 1?m Dissipative Soliton Fiber Laser Based On Micro/Nano Fiber Composite Waveguide

Mode-locked fiber lasers have the advantages of narrow pulse width,high average powerand high pulse energy,so they play an important role in many fields.Saturable absorbers(SAs)based on the nonlinear multimode interference(NL-MMI)have good damage resistance thresholds,and are suitable for high-energy mode locking of 1?m band fiber lasers.It is one of the current research hotspots of fiber lasers.However,for NL-MMI to achieve dissipative soliton mode locking in the full positive dispersion region,it is necessary to precisely control the length of the multimode fiber,and it is also necessary to introduce a filtering mechanism to achieve the dissipation effect in the cavity.The dissipative soliton mode-locked pulse has a strong positive chirp,which is accompanied by a larger pulse width.Therefore,the introduction of filtering mechanism and pulse compression to the dissipative soliton mode-locked fiber laser has also become a key issue.In this paper,offset-splicing multimode fiber(OS-GIMFs)combined with bismuth telluride(Bi₂Te₃)is used to obtain 1?m dissipative soliton mode locking,and micro-nano fiber dechirping is used to achieve pulse width compression.Finally,this article has carried out the following research contents around the above work:1.Analyze the ultrafast dynamic evolution process based on NL-MMI mode locking,and clarify the influence of its nonlinear saturable absorption characteristics on the optical pulse.The micro-nano fiber's compensation mechanism for intracavity dispersion is studied,and the micro-nano fiber is used to compress the dissipative soliton pulse in view of the large chirp characteristics of the dissipative soliton in the full positive dispersion region of the 1?m waveband.Because under the same wavelength condition,micro-nano fibers with different diameters will cause the dispersion of the waveguide to shift.Therefore,choosing a micro-nano fiber with an appropriate diameter can effectively control the waveguide dispersion,which is beneficial to realize the compression of the pulse width.2.Research on the composite structure mode locking of Bi₂Te₃ and OS-GIMFs.Firstly,the influence of different concentrations of bismuth telluride on the saturable absorption performance was analyzed to prepare high-performance Bi₂Te₃.Then the structure of OS-GIMFs is simulated to study the self-image effect and filtering effect of OS-GIMFs.At the same time,in the structure of OS-GIMFs,the degree of offset-splicing has a great influence on the filtering effect and insertion loss.By optimizing the structure of OS-GIMFs,a new structure that can realize dissipative soliton mode locking is prepared.Finally,the Bi₂Te₃is combined with the OS-GIMFs to form a composite structure.The results show that when the wavelength center is 1033.2 nm,the maximum output power is 4.16 m W,the pulse width is26.7 ps,and the signal-to-noise ratio is 53.8 d B.This composite structure effectively improves the output energy and stability of the dissipative soliton mode-locked fiber laser.3.Aiming at the pulse compression problem based on the dissipative soliton mode-locking of the composite waveguide,micro-nano fiber preparation process was optimized and improved,and the micro-nano fiber structure with a tapered waist diameter of 1.3?m was prepared by indirect heating.Connect it to the output end of a composite structure mode-locked fiber laser to compress the pulse width,and the final compressed pulse width is 2.3ps.