基于公共环形腔耦合的光纤激光器相干合成技术研究

To improve the combining efficiency, stability and expandability of passive self-adjusting coherent combining arrays of fiber lasers, a novel coherent beam combining scheme of fiber lasers is proposed based on a common fiber ring coupled cavity. The introduced ring cavity not only provides a common channel for mutual injection coupling among component fiber lasers, but also makes the coherent array own good expandability in structure. The early research results obtained in low power condition have primarily indicated that the scheme is feasible and preponderant. However, the combining effects in high power and large numbers need to be verified through further theoretical and experimental study. We intend to construct an experimental system based on the scheme to realize coherent combining of multiple high power Yb-doped double cladding fiber lasers, and establish the analytical model of the fiber lasers' coupling array when the effects of phase noise and multiple longitudinal modes are considered. Furthermore, the physical mechanism of passive self-adjusting phase locking of the coupling array is planned to be analyzed, and the effects of spectrum width, combining elements, pump intensity, mode competition and spatial filtering on the phase locking stability and combining efficiency are also arranged to be investigated, which are expected to solve the problem that whether the combining elements and output power are limited or not in the passive self-adjusting coherent combining scheme. These research works can provide significant reference for the development of laser beams' coherent combining techniques and laser array's coupling theory.

为提高光纤激光器无源自调整相干合成阵列的合成效率、稳定性和可扩展性，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。引入的公共环形腔不仅构成了激光器之间能量相互注入耦合的通道，也使阵列在结构上具有了良好的扩展性。前期小功率情形下的研究成果初步表明了该方案的可行性与优势，但在大功率多路数时的合成效果有待进一步的理论与实验研究来检验。利用该方案构建实验系统，实现多路大功率掺镱双包层光纤激光器的相干合成，建立考虑相位噪声与多纵模影响的光纤激光器耦合阵列理论模型，在 此基础上分析激光器耦合阵列无源自调整锁相的物理机理，研究激光束谱宽、合成路数、泵浦强度、模式竞争以及空间滤波等对锁相稳定性与合成效率的影响，解决无源自调整相干合成方案在合成路数与输出功率等方面是否受限以及如何受限等问题。研究成果可望对激光束相干合成技术、激光器阵列耦合理论等领域的发展起到一定的促进作用。

为提高光纤激光器无源自调整相干合成阵列的合成效率、稳定性和可扩展性，对基于公共环形腔耦合与相互注入耦合的光纤激光器被动相干合成技术进行了理论与实验研究。构建了多路掺铒和掺镱光纤激光器无源自调整相干合成的实验系统，在此基础上深入研究了耦合强度、多模运转、反馈元件和空间滤波等对锁相性能的影响。此外，建立了分析耦合强度影响的理论模型，并对模式竞争、克拉默-克隆尼克非线性相移等现象进行了分析，解释了多路光纤激光器无源自调整锁相的物理机理。研究表明，足够的能量耦合强度是获得有效相位锁定的必要条件，通过增加耦合比来增大耦合强度可以提高锁相阵列的相干性，但会略微降低合成效率；控制各激光束间的相位差恒定远比控制激光束的工作波长和偏振态重要，激光束的工作波长和偏振态可因模式竞争和能量耦合而自动调整，这为克服大功率光纤激光中的非线性效应和提高输出功率提供了新思路。