Research On All-fiber Passively Q-switched Ytterbium-doped Fiber Laser

Since Alcock introduced Q-switched technique into fiber laser in 1986,the Q-switched fiber laser has been one of the hot topics in the field of laser technology.The Q-switched fiber laser has the advantages of narrow pulse width,high peak power,high pulse energy,good beam quality and so on.In recent years,it has shown its unique application value in medical treatment,environmental remote sensing,laser ranging,industry production and other fields.There are two mainly methods to achieve Q-switched pulses: actively Q-switched technique and passively Q-switched technique.Passively Q-switched fiber laser without additional modulator has the advantages of compact structure,low cost,simple system,high efficiency and so on,which is one of the most important choice to obtain high repetition frequency,nanosecond and sub nanosecond laser pulse.Passively Q-switched Ytterbium-doped fiber laser are studied both theoretically and experimentally in this dissertation.On the theoretical side,the theoretical model of passively Q-switched Ytterbium-doped fiber laser is established.Meanwhile,the effect of different factors on the output characteristics of passively Q-switched pulse is investigated.Experimentally,two kinds of passively Q-switched Ytterbium-doped fiber lasers are built,and the pulse characteristics of the two lasers are analyzed and compared.The main points can be concluded as follows:1.We explain fundamental principles of Q-switched technology,and lay special stress on outlining fundamental principles of passively Q-switched technology.And the working characteristics of different saturable absorbers are also summarized.2.We simulate the characteristics of the passively Q-switched fiber laser byMatlab and analyze the results.The theoretical model,transfer function and rate equation of passively Q-switched Ytterbium-doped fiber laser are established.Subsequently,the effects of the pump power,the length and doping concentration of the saturable absorber on the characteristics of the laser are investigated by simulation.3.Based on the simulation results,we set up a passively Q-switched Ytterbium-doped fiber laser with a single-cavity structure.The influence of the pump power and the length of the saturable absorber on the output characteristics are analyzed and discussed.In the condition of the saturable absorber's length is 2m and the pump power is in the range of 660mW-1.5W,the minimum pulse width of the laser is 4.8?s.Meanwhile,the central wavelength of the Q-switched pulse is 1064 nm.4.In order to obtain stable passively Q-switched pulse,we construct an all-fiber passively Q-switched Ytterbium-doped fiber laser with a linear dual-cavity structure.This laser utilizes the passively Q-switched technique and gain-switched technique.The pulses can be obtained with the minimum pulse duration is 2.6?s and the repetition rate tunes from 13.23 kHz to 40.6kHz.The central wavelength of the smooth and stable pulse is 1064 nm.The influence of the length of the saturable absorber on the characteristics of the pulse is also discussed.Compared with the single-cavity passively Q-switched Ytterbium-doped fiber laser,the stability of the dual-cavity passively Q-switched Ytterbium-doped fiber laser is improved.To ensure the stable and efficient output of the pulse laser,the passively Q-switched and gain-switched Ytterbium-doped fiber laser can be used as a new choice for high performance pulse generation.At the end of the paper,we have summarized the main work of the paper and eventually the summary is made.