Dissipative Soliton Resonance Tm-doped Fiber Laser Based On NALM

In recent years,2 μm laser in the eye-safety band has shown unique advantages in many fields such as medical treatment,atmospheric detection and bioengineering.With the development of 2 μm fiber component manufacturing technology,the simple structure,economical and practical thulium-doped fiber laser has become an efficient laser source in 2 μm band.The passive mode-locked thulium-doped fiber laser can be used not only as an excellent 2 μm nonlinear fiber optical research platform,but also as a seed source for high-power 2 μm laser system.The dissipative soliton resonance pulse with high energy and difficult to split is an ideal pulse type for laser amplification system.Therefore,thulium-doped fiber laser based on nonlinear amplifying loop mirror is designed and constructed in this paper to study the dissipative soliton resonance pulse.The main contents include:(1)Literature research is carried out from two directions: thulium-doped fiber laser and dissipative soliton resonance.The representative results of dissipative soliton resonance pulse in both theoretical and experimental directions are summarized.(2)Based on the gain characteristics of thulium-doped fiber several pumping methods are introduced.The mode-locking mechanism of the nonlinear amplifying loop mirror in thulium-doped fiber laser is discussed according to its working principle.Two methods of solving the cubic-quintic complex Ginzburg-Landau equation are studied and the evolution of dissipative soliton resonance in laser is analyzed.(3)A passive mode-locked thulium-doped fiber laser is designed and built,which outputs two different dissipative soliton resonance pulses with a central wavelength of 1960 nm and a repetition frequency of 2.532 MHz.The pulse width and single pulse energy of the two pulses increase linearly with the pump power.At the maximum pump power of 2.4 W,the average output power of two pulses is 113.5 m W,and the corresponding single pulse energy is 45 n J.Then,the reasons for the difference of pulse width and peak power under the same pump power are analyzed according to the working principle of the nonlinear amplifying loop mirror.In order to further study the output characteristics of dissipative soliton resonance pulse,a laser cavity length comparison experiment is carried out.After the increase of the cavity length,the threshold of the two pulses mode-locking decreases,and the single pulse energy and pulse width increase with the same pump power.The single pulse energy and pulse width with cavity length of 95 m and pump power output of 2.4 W are 63 n J and 59.5 ns,respectively.By calculating the peak power of two pulses,it is found that changing the laser cavity length cannot improve the peak power of pulse.(4)In order to improve the peak power of the two pulses,a thulium-doped fiber amplifier is designed and built,but the amplified dissipative soliton resonance pulse could not be obtained.The problems are discussed in the experiment by numerical simulation of 793 nm pumping theory model.By setting the parameters in the simulation as experimental parameters,the gain fiber used in the experiment is so short that the unabsorbed pump light interfering with the excitation emission of 2 μm.Finally,the seed light is not amplified.