Design And Experimental Study Of Tunable Dual-Wavelength Single-Longitudinal-Mode Ytterbium-Doped Fiber Laser

The dual-wavelength single-longitudinal mode fiber lasers have recently been favored for their excellent performances,as will be found wide applications in the fields such as laser interferometric measurement,fiber sensing,and fiber communication,etc.Especially in the application of the synthetic-wave absolute-distance measurement,the multistage synthetic wavelength can be generated by using the tunable and large frequency-difference dual-wavelength single-longitudinal mode fiber laser as the light source,so that the high precision absolute-distance measurement can be achieved by using the step by step measurement method.Therefore,the dual-wavelength single-longitudinal mode fiber laser with tunable frequency difference is of great research significance and broad application prospects.In the thesis,a frequency-difference-tuned dual-wavelength single-longitudinal mode ytterbium doped fiber laser system,which is based on a linear resonant cavity structure,has been proposed and designed.Polarization maintaining fiber Bragg grating(PMFBG)is used as both dual-wavelength selector and wavelength-difference tuning element.The unpumped ytterbium doped fiber(UPYDF)is employed as a saturated absorber to select single longitudinal mode;By applying transverse force to the PMFBG,the frequency difference tuning of the laser can be achieved.The thesis mainly includes the following contents:Firstly,the research status of dual-wavelength single-longitudinal mode fiber laser have been reviewed.The ytterbium-doped fiber laser system,operating principle and the basic characteristic have been described;The energy level structure of ytterbium has been introduced.Secondly,after analyzing and comparing various dual wavelength generation and longitudinal mode selection methods,PMFBG is selected as the dual wavelength oscillation element and wavelength difference tuning element,and UPYDF is used as the saturated absorber to accomplish in selecting single longitudinal mode.A tunable dual-wavelength single-longitudinal mode ytterbium-doped fiber laser system is designed and its feasibility analysis is conducted.Thirdly,a dual-wavelength single-longitudinal mode ytterbium doped fiber laser system has been built.The experiment mainly has studied the dual wavelength oscillation and switching characteristics,saturation absorber mode selection,dual wavelength single longitudinal mode laser power and polarization characteristics.The experimental results show that the laser can achieve stable orthogonal linearly polarized dual-wavelength single-longitudinal mode laser oscillation at 1064.204nm and 1064.934nm,wavelength difference of 0.27nm,laser threshold pump power of 31mW.And a linear correlation between output power and pump power is observed.Besides these,adjusting the intracavity polarization controller can finish switching between single wavelength and dual wavelength.Finally,the experimental system of tunable dual-wavelength single-longitudinal mode ytterbium doped fiber laser is constructed.The piezoelectric ceramic actuator is selected as the component to generate the transverse force for PMFBG.The transverse force of PMFBG can be adjusted by changing the voltage of the electric ceramic driving power supply When the driving voltage of the piezoelectric ceramics is 0～75V,the wavelength difference tuning range of the dual-wavelength single-longitudinal mode ytterbium-doped fiber laser is 0.278nm～0.356nm,and the corresponding frequency difference tuning range is about 73.6GHz～94.3GHz.In summary,the tunable dual-wavelength single-longitudinal mode ytterbium doped fiber laser system designed is feasible.And this kind of dual-frequency fiber laser has bright application prospect in synthetic wave absolute distance interferometry and other fields.