可饱和吸收体是激光器的重要锁模器件。近年来，由于石墨烯作为饱和吸收体所具有的超宽的工作波段、超快的恢复时间、低的线性吸收、高的损伤阈值、可控的调制深度和较低的成本等特点而受到了人们的广泛关注。自从2009年石墨烯首次应用于光纤激光器中的锁模以来，石墨烯作为锁模器件在光纤激光器中的应用越来越广泛。本文利用石墨烯作为锁模器件，实现了在不同波段光纤激光器中的锁模，论文的主要内容包括：介绍了石墨烯的结构、性能、制备方法和应用，阐述了石墨烯作为可饱和吸收体的特点以及石墨烯作为锁模器件在光纤激光器中的应用。基于改进的非线性薛定谔方程，在理想饱和吸收体的模型下数值模拟了锁模脉冲的产生，并分析了石墨烯的调制深度对脉冲输出特性的影响。用光诱导的方法把石墨烯转移至光纤端面，制备了石墨烯的锁模器件，对石墨烯的线性吸收、拉曼频移和调制深度等特性进行了表征。研究了石墨烯在掺铒光纤激光器中的锁模和谐波锁模，得到了重频频率为502.84 MHz的32阶谐波锁模，并对比了石墨烯锁模器件在不同损耗时锁模和谐波锁模的性能。把石墨烯薄膜的样品与光纤集成，应用在2 μm波段铥钬共掺光纤激光器中的锁模。研究了在较长腔时激光器的输出特性，实现了在铥钬共掺光纤激光器中的纳秒脉冲锁模，输出的单脉冲能量高达38.6 nJ，并总结了腔长和泵浦功率对激光器输出特性的影响。利用同一个石墨烯锁模器件实现了在掺镱（1 μm）、掺铒（1.5 μm）和铥钬共掺（2 μm）三个波段光纤激光器中的锁模，波长跨度近1000 nm，是目前在实验上得到的波长跨度最宽的锁模结果。
Saturable absorber is an important mode-locker for lasers. Recently, graphene as a saturable absorber has attracted much attention owing to its outstanding properties such as ultrabroad wavelength range, ultrafast recovery time, low linear absorption, high damage threshold, controllable modulation depth and low cost. Since the first application of graphene for mode-locked fiber lasers in 2009, the application of graphene as a mode-locker is becoming more and more extensive for fiber lasers. This dissertation achieved the mode-locked fiber lasers in different waveband by using the graphene mode-locker. The main contents include:The structure, properties, preparation methods and applications of graphene were introduced. We illustrated the characteristics of graphene as saturable absorber and the applications of graphene as mode-locker in fiber lasers. Based on the modified nonlinear Schr?dinger equation, we simulated the generation of mode-locked pulses and analyzed the impact of modulation depth of graphene on the output properties in the model of ideal saturable absorber.The graphene sample was transferred to fiber end by the method of optical driven. We produced the graphene mode-locker and measured its properties such as linear absorption, Raman shift and modulation depth. The mode-locking and harmonic mode-locking were studied in erbium-doped fiber laser based on grahpene saturable absorber. We obtained the 32nd harmonic mock-locking with the repetition rate of 502.84 MHz. Besides, we compared the performance of mode-locking and harmonic mode-locking of graphene mode-locker with different losses.After the graphene film was integrated into the fiber, the 2 μm band thulium-, holmium-codoped fiber laser was studied. We investigated the output properties of the laser with long cavity and achieved the nanosecond mode-locking in thulium-, holmium-codoped fiber laser. The output energy of the pulses reached up to 38.6 nJ. The impact of the cavity length and pump power on output properties was also introduced.We achieved the mode-locking of three wavebands in ytterbium-doped, erbium-doped and thulium, holmium-codoped fiber lasers by a single graphene saturable absorber device. The wavelength span closed to 1000 nm, which is the widest result for mode-locking experimentally at present.
