【作者】 陈昭喜；

【导师】 徐文成；

【作者基本信息】 华南师范大学 ， 光学， 2005， 硕士

【摘要】 光纤激光技术是非线性光纤光学的重要研究领域,由该技术实现的高质量超短光脉冲光源是未来超长距离、超大容量光通信系统的关键技术之一。虽然色散渐减光纤中高阶孤子非绝热压缩可以得到皮秒或亚皮短秒脉冲,但是利用这种光纤压缩技术获得的脉冲往往伴有较宽的基座。带有基座的脉冲在高码率光通信系统中传输时会导致相邻脉冲之间的干扰。利用非线性光纤环型镜的孤子整形可以实现消基座作用,而且可以对超短脉冲进一步压缩。另外,非线性光纤环型镜作为等效快速饱和吸收体,在光纤激光器,尤其是在掺铒光纤激光器中广泛应用于被动锁模技术中。本论文研究了利用色散渐减变光纤构成的非线性环型镜(DDF-NOLM)获得的超短脉冲特性,对不同光纤环长度的环型镜及不同输入功率得到的压缩脉冲进行了特性分析。在此基础上,提出了一种新的非线性光纤环型镜,研究了新型非线性光纤环型镜的开关特性以及超短光脉冲在其中的传输特性,获得了一些有意义的研究结果。论文共分五章:第一章:介绍非线性光纤环型镜的基本结构,总结非线性光纤环型镜的广泛应用,以及它的研究进展。第二章:分析了非线性光纤环型镜的工作原理,包括脉冲在光纤中的传输理论,耦合器的工作原理,光纤环的开关效应,及计算方法。第三章:在前面研究的基础上,提出新的光纤环结构,在多种方案中,找出最佳的结构。新的光纤环型镜由色散渐减光纤和常规光纤构成,用该结构的光纤环型镜对脉冲进行压缩,可以得到无基座,啁啾小,压缩因子大的超短脉冲,输出的超短脉冲能在常规光纤中稳定传输。与DDF-NOLM进行比较,新的光纤环型镜使用的光纤更短,获得的压缩因子更大。更多还原

【Abstract】 The study of fiber laser is a very important area for the nonlinear optical research, which is regarded as one of the key technologies for the generation of high quality ultra-short optical pulse that is needed for the modern long distance, ultra-high bit rate optical communication systems. Although it is possible to obtain picosecond or sub-picosecond optical pulse in a dispersion decreasing fiber by adiabatic soliton compression, the output pulse is not satisfying due to the wide pedestal accompanied with the pulse. The pedestal is harmful because it can lead to cross talk between pulses in a communication system. However, Nonlinear Optical Loop Mirror (NOLM) can be used to suppress that pedestal and compress pulses more properly. Moreover, NOLM, which can be used as a saturable absorber, has many important applications of passive mode lock technologies in optical fiber lasers, especially in Er-dropped fiber lasers. In this thesis, NOLM constructed by dispersion decreasing fiber (DDF-NOLM) is studied. The propagation properties of the optical pulse in DDF-NOLM are discussed detailedly, including the pulse evolution in the fiber loop mirror, the compression factors, the pedestal energy and the peak power of the output pulse. A new type of NOLM is also presented that constructed by a segment of conventional single mode fiber and a segment of dispersion decreasing fiber. The optical switching properties and the propagations of optical pulses in this new NOLM are also studied. Some useful conclusions are achieved.The thesis consists of 5 chapters:Chapter 1: Shows the basic structure of NOLM, presents the applications and the research history of the NOLM.Chapter 2: Analyzes the mechanisms of the NOLM, including thepropagation equations of optical pulse in fibers and the mechanism of optical coupler and the optical switch.Chapter 3: Proposes the new type of NOLM based on the previous studies and finds out the optimal structure of the new NOLM from several schemes, which is constructed by a segment of dispersion decreasing fiber and a segment of conventional single mode fiber. From this new type of NOLM, a compressed pulse without pedestal and nearly un-chirped, which can propagated stably in a conventional fiber, is obtained. In comparison with the traditional DDF-NOLM, the output pulse has higher compression factor with shorter fiber length.Chapter 4: Studies the propagation of femtosecond pulse in a DDF-NOLM. The results show that there exists a time delay between input pulse and the output pulse in DDF-NOLM due to the Stimulated Roman Scattering (SRS) effects. Moreover, it is shown that the third order dispersion of the DDF fiber contributes a lot to the time delay and that the negative third order dispersion is more favorable than positive one in depressing this time delay and in getting higher compression factor, higher peak power of the pulse and higher transmission ratio. In short, negative third order dispersion is better than positive one for pulse compression in DDF-NOLM.Chapter 5: Draws the conclusion and makes some prospective views.更多还原