High Repetition Rate Femtosecond Fiber Laser At1.5μm

High repetition rate fs pulse laser has significant value in aspects of optical frequencymetrology, high speed optical sampling, laser ranging and so on. Within the traditionaltechniques of generating high repetition rate laser pulse, the actively mode-locking requireshigh frequency signal generators and phase (or amplitude) modulators which would increasemanufacturing costs and complexity of the system, and the passively harmonic mode-lockingis less stable and has more timing jitter compared with fundamental repetition rate passivelymode-locking. Nonlinear polarization evolution (NPE), which has a very fast response time,can be used to achieve sub-100fs pulse directly. Moreover, this mode-locking technique canbe conducted in an all-fiber configuration, which facilitates the design of laser cavity bettertolerant to environmental vibrations. For the past few years, benefiting from the improvementof Yb doping technique, high fundamental repetition rate nonlinear polarization evolutionmode-locking fiber laser at1.0μm has been developed rapidly. However, it developedextremely slow at1.5μm limited by the dopant concentration of Er. Recently, our researchinstitute successfully drew Er/Yb codoped phosphate glass fiber with a net gain high up to5.2dB/cm, which is the ideal active medium for high fundamental repetition rate nonlinearpolarization evolution mode-locking all-fiber laser. Furthermore, some novel mode-lockingtechniques, such as the graphene mode-locking which has a ultrafast recover time (about200fs), a low saturable absorbing threshold, controllable modulation depth and so on, havegreat potential for generating high fundamental repetition rate pulse. Focusing on the Er/Ybcodoped phosphate fiber high fundamental repetition rate mode-locking laser, this dissertationwill finish the following issues:1. Introducing the basic structure and mode-locking theory of mode-locking fiber laser;Combining experiments with theories, analyze the tunability of optical spectrum, theself-starting ability and the sidebands of optical spectrum of the high gain fiber NPEmode-locking fiber laser, where the propagation model of NPE mode-locking laser is used tostudy the tunability of optical spectrum, the generalized path-average nonlinear Schr dingerequation is employed to analyze the self-starting ability, and the pulse trace model togetherwith the coupled complex nonlinear Schr dinger equations are applied to simulate the opticalspectrum sidebands of mode-locking pulse; In addition, the characteristics of Q-switchedmode-locking of high gain fiber NPE mode-locking laser is investigated experimentally.2. Optimizing the cavity of nonlinear polarization evolution mode-locking all-fiber laser, and achieve the following results: fs pulse with a fundamental repetition rate of101MHz andan average output power of115mW; fs soliton with a fundamental repetition rate of235MHzand a duration of159fs; Bound-soliton with a174MHz fundamental repetition rate. On thisbasis, we design the nonlinear polarization evolution mode-locking all-fiber laser with acompacted cavity only including two elements, and obtain105fs pulse with a325MHzfundamental repetition rate.3. Utilizing the optical deposition and graphene-polymer composite thin film methods tofabricate mode-locker, and realize mode-locking operation respectively. Based on theNPE+SESAM mixed mode-locking technique, we achieve312fs pulse at a fundamentalrepetition rate of409MHz from a fiber ring cavity which only48cm in length.