| At present,Fiber lasers have attracted great attention and found applications in the fields of materials processing,high-speed optical communications,biological medicine,military and national defense and scientific researches owing to the advantages of compact structure,high efficiency and stability.By 2020,the annual sales of fiber lasers has a growth rate of～14%steadily.In particular,pulsed fiber lasers are considered as one of the most promising laser sources since they have the intriguing features of higher peak-power,low-power dissipation and narrow pulse duration.However,the market share of pulsed fiber lasers is still not good enough.The possible reason could be concluded as:the commercial pulsed fiber lasers are mainly obtained by active Q-switched/mode-locked techniques.In the fiber laser cavity,they usually require to insert an amplitude modulator,which makes available the complexity and high cost of whole laser system.On the contrary,the passively Q-switched techniques can achieve the real sense of low cost and compact structure.Aiming at the frontier research field of realizing neodymium-doped high-performance passive Q-switched all-fiber laser,this paper conducts research centering on two main bands of 0.9μm and 1μm,theoretical and experimental analysis were conducted,and achieves a series of innovative results.In summary,the major innovative achievements of this thesis are summarized as follows:(1)A single-mode laser rate equation model was constructed for 920 nm of Nd3+-doped F-P cavity,based on the rate equations,by solving the Runge-Kutta equation,we have thoroughly analyzed the characteristics such as threshold and slope efficiency.Immediately following,the impact of pump power and modulation depth on the pulses of Q-switched are investigated.At the same time,we have theoretically analyzed laser maser mechanism under the condition of different cavity length,and providing theoretical basis for optimization of lasing performance.In the experiment,neodymium doped fibers with lengths of 2.2 m,2.4 m,2.8 m and 3.2 m not only functions as a saturable absorber(SA),but also provides an optical gain.It shows,the first demonstration of that an stable 919.8nm all-fiber self Q-switched laser was obtained when the Nd3+-doped fiber was selected with 2.8m.A compact self-Q-switched Nd3+-doped silica all-fiber laser near 920 nm is experimentally demonstrated for the first time.Under an 808 nm laser diode(LD)pumping,a pair of homemade cavity mirrors that include a FBG and a fiber end-facet mirror construct a compact and simple all-fiber resonator.Stable Q-switched operation was successfully achieved.The pulses of 919.8 nm generated at a threshold of 90 mW,and the maximum average power obtained was 8.56 mW and a pulse width concomitantly obtained was 1.62 μs.And especially,we have realized a pulse energy of 123.4 nJ.(2)Based on the theoretical simulation results,a 905 nm Q-switched mode-locking Nd3+-doped all-fiber laser was investigated.In the process of experiments,we could deliver a central wavelength of 904.8 nm and a FWHM(Full Width Half Maximum)of 0.35 nm was obtained.The width of the mod-locked pulse was about 5 ns,and the peak power can reach 17 W.Secondly,we recorded the single pulses FWHM(Full Width Half Maximum)of the 905 nm Q-switched mode-locking laser and output average power were obtained when the output coupling mirrors were selected with different transmittance rates(2.6%,9%and 35%@905 nm).Since the pumping power of the pump was only 250 mW,we will improve the pumping light power and make negative dispersion compensation in the cavity in the later stage,We hold some promise of success with implementing continuous mode-locking steadily,and also get ultrashort pulse output.(3)Passively Q-switched operation of Nd3+-doped all fiber laser was studied using two dimensional materials.In the theoretical simulation,the impact of SAs were analyzed of characteristic parameter modulation depth and initial transmittance on Q-switched performance by numerical solution of Runge-Kutta equation.Passively Q-switched operation of Nd3+-doped all fiber laser was applied at 1μm wave band by inserting the Bi2Se3,and dual-wavelength laser operation at 1065.8 nm and 1074.3 nm were obtained.Q-switching operation is achieved with increasing from 69.68 kHz to 205.2 kHz,the tuning range was relatively wide.Meanwhile,pulse width from 1.42μs down to 601 ns,and single pulse energy was 38.83 nJ,maximum average power output was 6.6 mW,respectively.(4)We have constructed a three-wavelength Q-switched Nd3+-doped all-fiber laser,and applied it to the Nd3+-doped fiber laser for the first time using tungsten sulfide as a saturated absorber,and obtained the three-wavelength lasers of 1081.9nm,1091.3nm and 1100.1nm.The Q-switched operation pulse repetition frequency could be changed from 53.8 kHz to 124.4 kHz linearly.The output power of the laser and the corresponding single pulse energy increase roughly linearly and was obtained the maximum value at the pump power of 250 mW,which were 8.9 mW and 71.5 nJ respectively.The spectral signal-to-noise ratio(SNR)was up to 60.76 dB,and a stable Q-switched laser was realized. |
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