Passive Coherent Combination Technology Of Pulsed Fiber Lasers On Ring Cavity Feedback

Besides excellent beam quality, high conversion efficiency, convenient heat management, and compact configuration, high power pulse fiber lasers have many advantages such as high peak power and high pulse energy, wide optional tunable range and adoptable spectrum, so they can be widely used in industrial processing, communications, medical and scientific research and so on. The progress of output power/brightness of pulse fiber laser has attracted much attention as a hotspot and a challenging goal in recent years. However, the output power from a single fiber laser is limited by the fiber nonlinear effects, thermal lens, pump brightness and thermal damage and so on. In order to scale the output power/brightness from fiber lasers, one way is to supress nonlinear effect with especially design for large mode area fiber. Another way is to increase the output power by coherent beam combination(CBC) of multiple fiber laser beams, which can greatly improved the total output power meanwhile maintaining near diffraction limited beam quality. In this dissertation, theoretical and experimental study on passive phase-locking CBC technology of Pulsed fiber lasers with ring cavity feedback is presented, which contains the following contents:Firstly, the characteristic and pulse propagation of Q-switched pulse fiber laser configuration is studied,a single high peak-power Q-switched all-fiber laser with tunable ns-us pulse durations and Hz-MHz repetition rates is introduced, the maximum extractable peak-power of 10 k W could be achieved at 100 Hz. The evolution of nonlinear effects is measured as different level SRS generate in turn and become supercontinuum while spectrally broaden over the spot of zero dispersion. So the safety parameter of the pulse is put forward.Secondly,the model of ring cavity pulsed fiber lasers is introduced by using semiclassical laser theory. The dynamics mechanism of optical feedback ring cavity is studied,such as self-organizated phase locking and polarization self-selection. The phase locking characteristics as vernier effect,lease common multiple,low phase difference and low threshold in passive phasing of pulse fiber lasers with an all-optical feedback loop is demonstrated respectively. The difference of the cavity length and the range of wave length play an important role in self-organizated phase locking of pulse fiber lasers. The method that broaden the range of wave length can increase the number of pulse fiber laser of CBC.Thirdly,the theoretical model is demonstrated by all-fiber ring CBC pulse laser configuration and polarized beam coherent combination of pulsed fiber laser experimentally respectively. The passive phase locking coherent combining of multichannel Yb-doped pulse fiber amplifiers is achieved with the ring compound cavity. Two configuration presented here provide a feasible technique for power scaling of high-power pulsed fiber laser and maintaining beam quality simultaneously. Flat-top pulse generation is realized by using all-fiber combining configuration which could lighten the impact of SRS. The output power is limited by the maximal working outpower of the last stage coupling component.Lastly, the method of power scalling is study with ring compound cavity,and “three mixed”scheme is put forward. Especially mixed laser of pulse and CW, gain competitive in same laser is argued theoretically and experimentally. Mixed laser has essential characteristics as good coherence and easy control to realize different mixed rate by adjusting intensity modulator. The different mixed rate,different frequency, different duty has different gain after being amplified. And the small part have more intensity increase. At last,the inducing conclusion is sum up for scaling of high-power pulsed fiber laser.