【作者】 雷兵；

【导师】 冯莹；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2009， 博士

【摘要】 高功率高亮度的激光源在工业加工、自由空间光通信、激光雷达和定向能等领域具有重要应用,光纤激光束的相干合成是获得这类激光源的重要技术手段,而共腔耦合是多路光纤激光器通过无源自调整过程实现相干合成的有效途径。无源自调整相干合成方案结构简单,易于实现,但合成阵列通常在稳定性、效率和可扩展性等方面存在问题。本文提出了基于公共光纤环形腔耦合与单模光纤滤波的光纤激光器阵列锁相方案,为提高无源自调整相干合成阵列的稳定性、效率和可扩展性提供了一种新而有效的技术途径。利用迈克尔逊型耦合腔进行光纤激光器的相干合成是一种公共外腔耦合式相干合成技术,具有公共外腔耦合和共线干涉合成方案的一些特点。本文主要针对这两种典型的共腔耦合式光纤激光器相干合成技术方案展开了理论与实验研究,所取得的研究成果主要有以下几个方面:1.提出了基于公共光纤环形腔耦合的光纤激光器相干合成方案。方案中采用全光纤结构的环形耦合腔并通过多端口并排发射相干激光束,使合成阵列的稳定性、效率和可扩展性得到了一定的提高;利用该方案在实验上成功实现了三路光纤激光器的被动锁相输出,获得了约90%的合成效率;将公共环形腔耦合结构应用于两路环形腔激光器与可调谐激光器的相位锁定,也获得了较高效率的锁相输出,表明所提的公共光纤环形腔耦合式锁相方案对环形腔与可调谐光纤激光器也是适用的。2.理论上建模分析了公共光纤环形腔的特性,确定了设计适于锁相的公共环形耦合腔时应遵循的基本原则,并结合实验研究结果得到如下结论:较佳的成环耦合比为20%～30%之间,且耦合比的少许偏差对锁相效果几乎没有影响。3.在共腔耦合锁相方案中引入了单模光纤滤波技术,使得激光束各发射阵元之间形成了稳定的相位关系,研究了单模光纤滤波在控制远场光强分布与提高锁相稳定性两方面的作用,指出了通过并排组合方式实现相干合成时采取空间滤波选模措施的必要性。4.提出了f‐f结构的迈克尔逊型耦合外腔,并在理论上分析了该耦合外腔的能量传输特性,找到了调节外腔时需要重点控制的误差量。采用f‐f结构的迈克尔逊型耦合外腔,在实验上实现了两路光纤激光器的相干合成,并验证了f‐f结构的耦合外腔在增强单元激光器间的能量耦合与提高合成效率方面的作用。5.运用薄膜光学中的特征矩阵分析法,研究了迈克尔逊型耦合腔中分束器的相移特性,推导了两束相干光经过分束器分束后进行相干叠加时相位应满足的普适关系,并从物理机理上解释了分束器一侧发生相长干涉时另一侧必然发生相消干涉这一实验现象。更多还原

【Abstract】 The laser sources with high brightness and high average power have significant applications in many fields, such as industrial machining, free space communications, laser radar and directed energy. Coherent beam combining of multiple fiber lasers has been expected to be an important technique to obtain a laser source of this kind, and coherent combining of multiple fiber lasers with common cavity coupling configuration is an effective approach by passive self-adjusting process. The passive self-adjusting coherent combining schemes usually own simple configuration and are easy to implement. However, the combined coherent array based on the above mechanism often suffers from the poor stability, combining efficiency and expandability. A novel phase locking scheme of fiber lasers is proposed based on common ring coupled cavity and single mode fiber filtering, which provides a new and effective method to improve the stability, efficiency and expandability of the general passive coherent array. Coherent combining of fiber lasers utilizing Michelson-type coupled cavity is a scheme based on common external cavity coupling, which owns the properties of both common external cavity coupling and collinear interferometric schemes. These two coherent combining schemes of fiber lasers with common cavity coupling configuration are investigated theoretically and experimentally in this paper, and the main achievements are listed as follows:1. The coherent combining scheme of fiber lasers based on the common fiber ring coupled cavity is proposed. Thanks to the all-fiber structure of ring coupled cavity and multiple parallel emitting ports, the stability, efficiency and expandability of combined array are improved evidently. Phase locking of three fiber lasers are demonstrated by using this scheme, and nearly 90% combining efficiency is obtained. The common ring coupled cavity is also employed to lock the phases of two ring cavity lasers and tunable fiber lasers, and the phase locked output with relatively high efficiency is also obtained, which indicates that the proposed phase locking scheme is compatible with ring cavity and tunable fiber lasers.2. The properties of the common fiber ring cavity are analyzed theoretically, and the basic principles when design a suitable common ring coupled cavity are summarized. Some crucial conclusions obtained from the theoretical analysis and experimental study are presented as follows: the optimized coupling ratio of constructing the ring cavity is in the range of 20% ~ 30%, and the small derivation of coupling ratios has little effect on the phase locking results.3. The single-mode fiber filtering technique is introduced into the proposed phase locking scheme with a common cavity, and relatively stable phase relation is formed among the multiple laser emitters. Both the actions of controlling the far-field intensity distribution and improving the phase locking stability are investigated, and the necessity of adopting the spatial filtering and mode selection measures when utilizing the side-by- side combining methods to realize efficient coherent combining are pointed out.4. The Michelson-type coupled cavity with an f‐f?configuration is presented, and its power transmission properties are analyzed theoretically, and the cavity errors which need to be paid more attention to decrease them when adjust the cavity are discovered. Moreover, coherent combining of two fiber lasers using the Michelson-type coupled cavity with an f‐f? configuration is demonstrated under low power condition, and the cavity’s functions of enhancing the energy coupling among individual fiber lasers and improving the combining efficiency are also verified in experiment.5. The phase shift properties of the beam splitter in Michelson-type coupled cavity are studied by the eigen-martix analyzing method in Optics, and the general relationship between the phase shifts of two splitted beams used for coherent combining is obtained, and then the experimental phenomenon that when the constructive interference occurs at one side of the beam splitter and the destructive interference has to occur at its opposite side is explained according to its physical mechanism.更多还原