Research On Single Frequency Yb - Doped Fiber Laser Based On Ring Filter

Single frequency fiber laser refers to the fiber laser that there is only one longitudinal-mode output in its resonant cavity, so it is also called single-longitudinal-mode fiber laser. Because of its high conversion efficiency, good coherence, compact structure, narrow line width and other characteristics, single frequency fiber laser has a wide range of applications in the field of optical communications, optical sensors, precision measurement. In this paper, we combined the fiber loop mirror and saturable absorber in the linear cavity to achieve single frequency fiber laser output at 1064 nm, and after that we used single frequency laser as the seed to have power amplification, the main work and research are below:1.We analyzed the energy level structure and spectroscopic properties of Yb-doped fiber in theory, and also calculated the optimum fiber length and power distribution in the linear cavity. Based on the principle of fiber loop mirror, we put a saturable absorber into it to form a loop mirror filter, and had a theoretical analysis of the filtering principle and the formation mechanism of dynamic grating. Besides, we also explained the reason that graphene could be used as saturable absorber in the single frequency fiber laser and loop mirror filter.2.We combined the fiber loop mirror and saturable absorber in the linear cavity to achieve single frequency fiber laser output at 1064 nm. We used Yb-doped fiber and graphene as the saturable absorber in the fiber loop mirror respectively, and continuously adjusted the polarization controller to achieve a stable single frequency laser output at the center wavelength of 1064 nm. Finally we obtained a power stability of more than 98%, the signal to noise ratio of 60 dB. When ytterbium-doped fiber was saturable absorber the laser threshold was 30 mW, the maximum output power was 32 mW and the slope efficiency of 33.8%.When the graphene was saturable absorber, the laser threshold was 26 mW, the maximum output power was 16 mW and the slope efficiency was 15%. The line width measured by delay self-heterodyne method was 5 kHz.3.After achieving stable single frequency laser, we used its output signal as the seed to amplify power. In the MOPA power amplification system, we respectively used the 2 m,5 m, 10 m of Yb-doped fiber as the gain medium, by comparing the results, we found that the output power was the highest when the fiber was 5 m, and the maximum amplification power was 160 mW when the corresponding pump power was 300 mW, the gain coefficience is 14.3 dB, magnification times was 26.7.