Investigations Of The Techniques For Figure-9 Ultrafast Fiber-Laser

Ultrafast laser technology is widely used in scientific research,industry,biomedicine and other fields.With the development of pulse evolution mechanism and mode locking mechanism,ultrafast fiber laser has gradually occupied a place in the field of ultrafast laser due to its low cost and easy maintenance.Among them,Figure-9 ultrafast fiber laser based on nonlinear amplification loop mirror mode locking has the advantages of self starting,low noise and high stability.Improving the performance of Figure-9 ultrafast fiber laser is of great significance to the development and expansion of ultrafast fiber optics.This paper focuses on the characteristics of Figure-9 ultrafast fiber laser with many different pulse evolution mechanisms.The main contents include:Firstly,the principle and research status of ultrafast fiber laser based on different saturable absorbers and intracavity pulse evolution mechanism are discussed.One of the difficulties in the field of ultrafast fiber laser is the development of mode-locked fiber lasers which can self-start and operate stably for a long time.Based on this,the research status and existing problems of Figure-9 fiber laser are described,and the mode locking principle and structure of Figure-9 ultrafast fiber laser are described.The evolution behavior of pulses in solitons,dispersion managed solitons,dissipative solitons and narrowband dissipative solitons figure-9 fiber lasers is numerically analyzed;Secondly,the factors limiting the narrowing of ultrashort pulses in Figure-9 ultrafast fiber lasers are proposed for the first time.Analytical analysis and numerical simulation analysis of the dispersion-managed Figure fiber laser are carried out,and the following conclusions are obtained:There are two-way transmission pulses in the Figure-9 fiber laser,and the output pulse is the result of coherent synthesis of the two-way transmission pulses.The quality and width of the coherent combined pulse are related to the two-way transmission pulse parameters such as pulse width,amplitude and carrying chirp and other parameters,which are difficult to comprehensively optimize;experimentally,we have achieved a 55fs pulse output,which provides a possibility for further narrowing of the pulse.The research on the pulse narrowing of the Figure-9 ultrafast fiber laser is of great value for the development of arbitrary wave generation,optical frequency combs,and high-speed optical sampling.Thirdly,research and clarify that the reason for the low output pulse energy of the Figure-9 fiber laser is the overdrive of the saturable absorber,and for the first time link the self-starting characteristics and overdrive characteristics of the laser with the characteristics of the nonlinear amplifier loop mirror;Based on our analysis,a method is proposed for the first time to increase the pulse energy of the self-starting Figure-9 ultrafast fiber laser by jointly adjusting the linear phase shift and the pump power.This method was verified in the dispersion management Figure-9 ultrafast fiber laser,which increased the pulse energy from the initial 0.36nJ to 1.4nJ.This method starts from the saturable absorption mechanism of Figure-9 laser for the first time,and solves the limitation of Figure-9 laser pulse energy.If this method is applied to dissipative soliton/amplified self-similar lasers and even large-mode fiber lasers,It is expected to achieve an order of magnitude increase in pulse energy,which is of great significance for the development of self-starting and environmentally stable high-power ultrafast lasers.Fourthly,the research status of low repetition rate near conversion limited picosecond pulse and the limiting factors of realizing low repetition rate pulse output are discussed.A scheme of realizing low repetition rate in near conversion limited picosecond figure-9 laser is proposed.The scheme of reducing repetition rate is verified by theoretical simulation and experiment,and the?20ps,848khz near conversion limited picosecond pulse output is realized;In this paper,different pulse evolution domains that can be realized by figure-9 ultrafast fiber laser are deeply studied,and two new methods are proposed to optimize the output pulse characteristics of figure-9 ultrafast fiber laser.The performance index of self starting and low noise figure-9 laser is broadened,which is of great significance to the field of ultrafast fiber laser.