980nm Photonic Crystal Fiber Picosecond Laser And Fiber Laser Coherent Combine Technical Study

Due to the excellent optical properties, pulse lasers have important applications in national defense construction, biomedical research, astronomical geography detection and advanced communication. As the novel third-generation laser,fiber laser has been developed rapidly in recent years. The output power of fiber laser cannot be improved continuously because of the limitation of the intensity of diode pumped laser. The Yb-doped fiber laser which has a high emission spectrum at 980 nm is expected to be used as the pump to largely improve the output power of Yb-doped/ Er-doped fiber laser and amplifier. At the same time, coherent combination of fiber laser is also an important technique in realizing high power and high beam quality fiber laser system.To obtain high output power fiber laser at 980 nm, large mode area photonic crystal fiber was used. The high power fiber laser with emission spectrum at 980 nm not only can be used as the pump, but its frequency can also be doubled to 490 nm which is beneficial to ocean detection and communication. We also increased the fiber output power by active control phase way to realize the fiber laser coherent combining technology and extended the application field of fiber laser. In this thesis, the main research work and results are as follows:In the first part, we summarize the reports related from both China and other countries on the pulsed fiber laser at 980 nm and give a brief introduction to principles and key points about Yb-doped fiber. Meanwhile, we also summarize the related developments from domestic and international developments on the coherent combining of ultrashort laser pulse by active phase control. All of these are the basis of the following experiments and corresponding analyses.In the second part, we theoretically analyze the influence of dispersion and nonlinear effect on pulse transmission in fiber cavity. Secondly, we also theoretically analyze the principles and influence factors of Yb-doped fiber laser excitation in three-level-system. Moreover, we analyze the process of pulse shaping, evolution by semiconductor saturable absorber mirror(SESAM) and nonlinear polarization evolution(NPE) technique. We compare the different function of the fast and slow saturable absorber for pulse formation.In the third part, we build a 980 nm passively mode-locking Yb-doped large mode area photonic crystal fiber oscillator with SESAM and NPE technique,simultaneously. The oscillator generates a maximum peak power of 4.6 k W with a repetition rate of 87.37 MHz. The pulse width is 1.24 ps and the output spectrum of the pulse is centered at 977.7 nm with a FWHM of 1.90 nm. From the results of the experiment, the direct output pulse close to the Fourier-transform limit. Secondly, a 980 nm Yb-doped photonic crystal fiber laser use a multilayer molybdenum sulfide polymer composite as broadband saturable absorber, which is prepared by the chemical vapor deposition method. It is the first time that Mo S2 Q-switched Yb-doped photonic crystal fiber laser at 980 nm has been demonstrated. Finally, 980 nm laser amplifier has been demonstrated using MOPA amplification technology and studied theoretically and experimentally.In the fourth part, pulse fiber laser coherent combined technology has been demonstrated on the theoretical and experimental research. The stochastic parallel gradient descent(SPGD) algorithm based on DSP has been designed into the circuit of phase feedback control. We establish a single-frequency fiber laser and ultrashort pulse fiber laser to test the performance of circuit and complete the two paths pulse fiber laser coherent combining, common phenomenon of coherence combined are also summarized.