折射率沟槽结构光纤激光侧面泵浦耦合特性研究

Fiber lasers became one of the most interesting research fields due to its high electro-optic conversion efficiency and high beam quality. Pump light reliably and efficiently coupled into a gain fiber is critical technology in the high power fiber laser with fiber pump coupler. There are several disadvantages in existing fiber pump coupler, for instance, large signal insertion loss, low backward isolation and mismatch with large-mode-area (LMA) fiber and so on. Moreover, the advanced technology is blockaded by foreign countries. There is a wide gap between the domestic technology and foreign technology, it is imperative to research and innovate independently in order to reach international advanced level. This project develops a new fiber laser side-pumped coupler with index valley configuration, and it is consisted of multi-pump fibers and a main fiber. Pump light transfers to main fiber through three coupling sections with high coupling efficiency. There is a refractive index valley in this coupler and the core of main fiber wasn't destroyed through fabrication process, which make this coupler have the advantages of low insertion loss of signal light, high coupling efficiency of pump light, high backward isolation and satisfaction with LMA fiber,etc. This project studies deeply coupling loss mechanism of the coupler modes by use of wide-angle beam propagation method with perfect match boundary conditions in the three-dimensional finite difference space, and provides direction for the coupler design and experiment fabrication. Secondly, we explore the fabrication technique of coupler, and grasp the full set of fabrication method. For the first time, we achieved a fiber coupler with the tolerance power of pumping light of 3 kW, continuous signal light of 1 kW and pulse signal light of 1MW.

光纤激光器具有转换效率高、光束质量好等优点，成为激光研究的一个热点。而如何将泵浦光通过光纤耦合器可靠、高效地耦合到增益光纤成为研制高功率光纤激光器的关键问题。现有光纤耦合器存在纤芯损耗大、反向隔离度低及无法应用于大模场光纤等问题；且国外对其实行严格技术封锁，国内外技术差距较大，急需自主研究创新以达到国际先进水平。 本项目提出的折射率沟槽结构光纤激光侧面泵浦耦合器，泵浦光经过三段耦合区高效地耦合到主光纤。此耦合器具有独特的折射率沟槽结构，在制作过程中不破坏主光纤纤芯，具备信号和泵浦光插入损耗小、反向隔离度高和可应用于大模场光纤等优势。本项目建立有限差分三维空间下完美匹配边界条件大广角光束传播方法，对耦合器模式耦合损耗机理进行深入研究，为耦合器设计及实验制作提供指导。其次，开展耦合器制作工艺探索，掌握全套制作方法，拟首次实现耐受功率为：泵浦光3kW，连续信号光1kW，脉冲信号光1MW的光纤耦合。

光纤激光泵浦耦合器是光纤激光器中的核心器件，直接决定激光器输出功率水平，国内外对此器件研究非常重视。我们针对光纤激光泵浦耦合器开展研究，提出了折射率沟槽侧面泵浦结构的光纤耦合器。首先，在理论上建立了有限差分三维尺度大广角完美匹配边界条件光束传输（FD-3D-PML-BPM）理论模型，深入研究了折射率沟槽侧面泵浦耦合器（Index Valley Side Pumping Coupler, IVSPC）泵浦光和信号光传输损耗特性，以及耦合器的反向隔离特性；分析了纤芯微形变对模式扰动特性机制，主要明确了信号光损耗和光束质量受纤芯形变影响；理论模型以及分析结果为IVSPC耦合器设计提供了指导。其次，实验上搭建了折射率沟槽结构光纤激光侧面泵浦耦合器制作工艺平台，完成了折射率沟槽结构光纤激光侧面泵浦耦合器制作工艺研究，掌握耦合器制作的关键技术工艺，成功制作了多种光纤搭配的耦合器样品。最终在应用上，将IVSPC耦合器成功应用到了各种脉冲和连续光纤激光器中，包括：调Q脉冲光纤激光器、LD作为种子的脉冲光纤激光放大器、锁模光纤激光器、3kW连续激光输出的光纤放大器以及新波长（1018nm、1030nm、ASE源和拉曼激光）光纤激光器中，验证了IVSPC耦合器的实用性和优越性。项目资助发表论文14篇，其中SCI检索12篇。培养博士生3名，其中1名已经取得博士学位，2名在读。