The Study Of Wavelength Tunable And Self-sweeping Narrow Linewidth Ytterbium-doped Fiber Laser

Because of its excellent monochromatism,low noise,high beam quality and long coherent length,narrow linewidth fiber lasers have important applications in the fields of gravitational wave detection,object displacement measurement,ranging system,laser communication,optical sensing,laser cooling and coherent light synthesis.In recent years,narrow-linewidth fiber lasers have been extended to dual-wavelength,multi-wavelength and wavelength tuning in order to meet the needs of applications in different scenarios such as microwave signal generation,WDM system and coherent spectrum synthesis.The realization of the spectral tuning characteristics of narrow linewidth fiber lasers has always been a hot research direction in this field.On the one hand,traditional wavelength tuning methods such as temperature-controlled fiber Bragg grating(FBG),tunable bandpass filter and Lyot filter based on optical polarization characteristics are widely used in fiber lasers.On the other hand,the tuner based on the electric drive can realize the time dependence of the laser output wavelength to obtain the sweep output.In addition,the tuning method based on the dynamic induced grating in gain fiber is also being actively explored.This thesis mainly uses the dynamic grating formed in the doped fiber to construct the ultra-narrow band pass filter and realize the wavelength tuning output of the ytterbium-doped fiber laser in the narrow linewidth state.First,a double circulator interferometer was constructed,and an unpumped ytterbium-doped fiber to form a dynamic induced grating and a panda-type polarization maintaining fiber to form a comb spectral filter were respectively embedded in it.The double circulator saturable absorber filter and the double circulator comb spectrum filter are respectively placed in the fiber laser resonator to obtain a stable single-frequency narrow linewidth laser output.Then,the research of wavelength self-sweeping ytterbium-doped fiber laser was carried out.In the ytterbium-doped fiber ring cavity,no isolator or optical components that limit the laser output direction are used to make the laser operate in both directions in the cavity to form a bidirectional standing wave cavity structure.The self-sweeping operation of the output wavelength is obtained in the single-mode fiber structure and the polarization-maintaining fiber structure.By studying the behaviors of self-sweeping laser generation,a stable single-wavelength single-frequency output is obtained in a all-polarization-maintaining cavity.Last,a new type of single-frequency self-sweeping fiber laser with new intensity dynamics is also realized in Ytterbium-doped fiber based on fiber saturable absorber.The main work and innovative achievements of this paper are as follows:First,we weld in the binary editor single-mode ytterbium doped fiber built binary saturable absorber filter,one aspect can be increased by double cavity structure cavity model of longitudinal mode interval operation,on the other hand the embedded optical fiber saturable absorber can form stable under the action of a standing wave field unb single-mode laser induced grating to stable operation.In the case of the fiber optically adjustable bandpass filter,we obtain the wide tuning narrow linewidth low noise ytterbium doped fiber laser.In addition,we fused 1 m polarizing Panda fiber in the same double circulator,and the inherent refractive index difference of polarized fiber would lead to the interference of laser to form a dressing spectral filter.We have calculated and measured the spectrum of dressing theoretically and experimentally.The parameters of the experiment are optimized,and the spectral overlap of the dressing spectrum and the bandpass filter is adjusted by the polarization controller to achieve the broadband tuning output.Compared with the single-frequency fiber laser realized by the double-circulator saturable absorber,we extend the tuning range of the laser and obtain a higher tuning range in the short wave.The output signal to noise ratio of 50 d B,the line width is also greatly narrowed.Secondly,we have experimentally studied the bidirectional cavity self-sweeping ytterbium-doped fiber laser.The self-sweeping effect has been observed in the single-mode structure and the all-polarization-maintaining structure,and its behaviors have been summarized.The sweeping range from 1038.98 nm to 1036.23 nm is obtained in the single-mode bidirectional cavity structure,and the average sweeping speed is 0.38 nm/s.The self-pulse signal in the range of 116.1 k Hz to 128.3 k Hz can be observed when the fiber laser works in the self-sweep state.In all-polarization-maintaining structure,two output couplers with different ratios of 10/90 and 50/50 were used to observe the self-sweeping effect and summarized.In the 50/50 output coupler,the wavelength of the laser output center is swept from 1060.468 nm to 1052.984 nm,and the average pulse repetition rate ν increases with the increase of the square root function of the total output power P.The sweeping rate α decreases with the increase of total output power P.In the10/90 output coupler,the ultra-slow self-sweep phenomenon with sweeping rate of 16pm/min ranging from 1070.448 nm to 1066.026 nm is produced,and the intensity dynamic display pulse signal is discontinuous in the ultra-slow self-sweep state.Furthermore,a self-sweeping fiber laser with flexible wavelength based on the loss adjustment in the cavity caused by the curved fiber circle is studied.The self-sweeping effect is achieved by a bidirectional laser cavity.The diameter of the circle is adjustable for loss.As the diameter decreases,the sweeping range can cover 1055.6-1034.6 nm,the initial wavelength decreases and the threshold power increases.This simple method may improve the sweep performance of various doped fiber lasers without increasing the consumption and cost.Thirdly,based on the above research on bidirectional cavity ytterbium-doped fiber laser,a stable bidirectional cavity single-frequency ytterbium-doped fiber laser is obtained by adjusting the parameters in the bidirectional cavity.During the wavelength monitoring of the laser over two hours,the wavelength fluctuation of the laser is less than 0.02 nm.At the same time,its intensity dynamically shows stable sine wave modulation.There is a stable phase difference between the clockwise laser output and the counterclockwise laser output.The bidirectional cavity single-frequency ytterbium doped fiber laser has a slope efficiency of 47.9% from the laser threshold to 90 m W and a linewidth of 7.43 k Hz is measured.The laser has the advantages of unique intensity dynamic,narrow linewidth,low threshold,simple structure and easy operation,which has better practical value.Fourthly,a novel self-sweeping fiber laser based on a fiber saturable absorber is studied for the first time.In a simple ring cavity,a fiber saturable absorber with fiber ring mirror,namely 1.8 m ytterbium doped fiber,are introduced by the use of circulator.When there is no wavelength selector in the cavity,the optical fiber laser generates wavelength self-sweep phenomenon,and the maximum self-sweep range of the center wavelength of the laser is from 1066 nm to 1071 nm.However,the intensity dynamics of lasers show a completely different phenomenon.By studying the time-domain pulse variation and wavelength self-sweep speed under different pump power,we find that the consistency between the two is found by calculating the interval of wavelength variation and the length of the laser cavity.Furthermore,the theoretical explanation and analysis of the time domain pulse are given.