基于二维材料和改进NPR的被动锁模光纤激光器研究

Abstract

Passive mode-locked fiber lasers become a hot topic due to their important applications in many fields,such as fiber sensors,biomedical research and nonlinear https://www.360docs.net/doc/fc18244111.html,pared with other lasers,fiber lasers have some advantages like anti-electromagnetic interference,small size and simple structure.Recently,saturable absorber and Nonlinear Polarization Rotation(NPR)effect are two effect schemes to generate mode-locked pulses.However,both schemes can only control the polarization state in the cavity.In this paper,we studied on the properties of saturable absorber and NPR effect mode-locked fiber laser.Meanwhile,after discussed the disadvantages about them,an improved NPR structure had been design.It can increase the controllable variables in the cavity.Also,the output characteristics of the mode-locked fiber laser had been extended.

For the diversification of mode-locking methods and two-dimensional materials, we respectively experimented on Bismuth Selenide,Molybdenum Disulfide and Black Phosphorus by three different production schemes.The saturated absorption characteristics of them have been understood well.Due to the limitations of fabrication process,the Molybdenum Disulfide taper fiber and the Black Phosphorus film produced by mechanical delamination were difficult to get the mode-locked pulse output. Fortunately,we achieved the picosecond mode-locked soliton output by using the Bismuth Selenide film.It helps us understand the saturation absorption effect deeply. However,the mode-locked device made by this method has only one controlled variable in the cavity and the life expectancy are lower,reducing the laser performance.

For the disadvantage of Saturable Absorber,we propose a new mode-locked fiber laser with improved NPR structure.A Variable Optical Attenuator was used to increase the dimension of the controllable variable in the cavity.Through repeatedly increasing and decreasing the cavity loss,the mode-locked pulse of picosecond order can be generated.Moreover,the mode-locked pulse output of the bound soliton can be achieved when increasing the pump power.The order of the highest bound states reaches21,which greatly enriches the output characteristics of mode-locked pulses.The use of such an improved NPR structure can increase the performance of lasers.Also,the mode-locked pulses can be obtained more easily under the control of multiple controllable variables and the laser operating state are more stable.

Thus,we further combine the improved NPR structure with high nonlinear fiber to realize high-performance dual-wavelength mode-locked fiber laser with adjustable repetition rate.The experiments show that the adjustable attenuator will not affect the performance of highly nonlinear optical fibers.By precisely adjusting the VOA in the cavity,a dual-wavelength bright-dark soliton pair with1-11orders tunable repetition

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rate and a dual-wavelength mode-locked soliton with1-22orders adjustable repetition rate were obtained.Moreover,he dual-wavelength bright-dark soliton pair have two wavelengths with orthogonal polarization.Through carefully changing the polarization state of cavity,the bright and dark wavelengths can convert to each other.In other words,we get a tunable dual-wavelength pulse output.

The research work in this dissertation provides an important idea to design a multi-purpose passive mode-locked fiber laser.It has been an important reference in the application of saturable absorber and NPR mode-locking technology. Keywords:two-dimensional materials,nonlinear polarization rotation,mode-locked fiber laser

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