Research Of 3?m Passively Mode-locked Fiber Laser And Broad Band Supercontinuum Generation

3 ?m ultra-short pulsed laser has a wide range of applications in military,medical,scientific and technological fields.At present,it has been used in spectroscopy,remote sensing,frequency metrology,free-space communication,laser surgery,light detection and ranging,missile countermeasure and high-efficiency pump sources for longer-wavelength oscillators.Because the fiber laser has the characteristics of simple and compact structure,high stability,good heat dissipation,high beam quality and low cost,3 ?m mode-locked fiber laser is an important development direction in the field of laser,which has attracted much attention from researchers in this field.In this dissertation,the numerical simulation and experimental investigation of 3 ?m passively mode-locked fiber laser are presented.In the part of numerical investigation,firstly,we derived the coupled Ginzburg Landau?G-L?equation which is used to describe the evolution of the laser pulse propagating in the gain fiber.Secondly,the mechanism of passive mode locked fiber laser based on saturable absorber?SA?and NPR structure is analyzed,and the mathematical model of passive mode locked fiber laser with different cavity and different mode locking principle is established.Finally,based on the mathematical model of the mode-locked fiber laser,3 ?m passively mode-locked Ho³⁺/Pr³⁺ co-doped ZBLAN fiber laser is numerical studied.The results show that when inserting a SA into the cavity of NPR mode locked fiber laser,the limit of the gain fiber length,pump souce power and laser polarization state in cavity is more relaxed,so through adjusting the polarization wave plate,the stable mode-locked pulse output is easier to obtain.In the experimental investagation part,we fabricated high quality multilayer black phosphorus?BP?materials with liquid phase exfoliation?LPE?method,and produced a BP SA with modulation depth of 41.2%,saturation peak intensity of 3.767MW/cm2.Based on the BP SA,we obtained the 2866.7 nm mode-locked pulse with pulse width of 8.6 ps,repetition frequency of 13.987 MHz,pulse energy of 6.28 nJ and output average power of 87.8 mW.It has successfully proven the possibility of fabricating two-dimensional material BP as SA for 3 ?m band.In addition,we tried to build a 3 ?m mode locked Ho³⁺/Pr³⁺ co-doped ZBLAN fiber laser based on NPR + semiconductor saturable absorber mirror?SESAM?hybrid structure.The results show that the NPR structure of the hybrid mode locked fiber laser does not play the role of equivalent SA,only SESAM plays a role of pulse modulation to generate the Q-switched pulse.Through the experiment and simulation investagation,we analyzed the reason of this phenomenon and give the improvement scheme of the fiber laser system.In the hybrid mode-locked fiber laser system,when the pump power can not be further enhanced,in order to generate mode-locked pulse output with NPR + SESAM hybrid structrue,we should choose low saturation energy SESAM,and should give full consideration to the intra-cavity maximum pulse intensity level for designing gain fiber length.At last,we designed three high nonlinear As2S3 suspended-core fiber?SCF?,which is suitable for using 1550 nm,2000 nm and 2870 nm pulse lasers as the pump source to generate supercontinuum?SC?,respectivly.Based on the generalized nonlinear Schrodinger equation?GNLSE?,SC generation in the three designed fibers is simulated and optimized.Through optimization,in the simulation research,using 2870 nm mode locking pulse as seed source,we obtained the mid infrared SC spaning over 1.5 ?m to 13 ?m in the As2S3 SCF with core diameter of 5 ?m,zero dispersion wavelength?ZDW?of 2825 nm.