基于玻璃分相技术的高掺杂石英光纤及其窄线宽激光研究

Narrow linewidth fiber laser, due to its narrow linewidth and single longitudinal mode, which has wide applications in fiber communication, fiber sensing, laser radar. Heavily doped phosphate fiber has been used as the main gain medium for narrow linewidth fiber laser. Considering that the quartz glass has better thermal stability and compatibility, it is of great academic value and scientific significance to develop heavily doped silica fiber as the gain material. However, clustering of rare earth ions in the quartz glass limits the development of heavily doped silica fibers and corresponding narrow linewidth fiber lasers. This project aims to prepare heavily doped silica fiber for high power narrow linewidth fiber laser based on the glass phase-separation technology. The project will focus on some significant questions，including: study on the dependence of clustering of rare earth ions on the factors such as nano-pore distribution of porous glass, size, shape and other multi-coupling parameters; analysis of the mechanisms of promotion or limitation clustering of rare earth ions by codoping of aluminum ions, phosphor ions and other codopants; revealing the clusters dynamic processes in the nanochannel of nanoporous silica glass; exploration of the preparation method of heavily doped silica fibers with core material as nanoporous silica; study on the spectroscopic properties and laser characteristics of the heavily doped silica fiber. Based on the above research, it will be beneficial to reveal the cluster mechanism of rare earth ions in the quartz glass, to open up new routes for the heavily doped silica fiber, to provide critical materials for high power narrow linewidth fiber lasers.

窄线宽光纤激光器因其独特的线宽优势，在激光雷达、光纤通信、光纤传感和相干通信等领域具有广泛应用。一直以来，高掺杂磷酸盐基质光纤作为窄线宽光纤激光器的主要增益介质获得成功应用。然而，窄线宽光纤激光器对温度、振动等异常敏感。考虑到石英玻璃具有更好的热稳定和兼容性，因此发展高掺杂石英基光纤，对窄线宽光纤激光器发展具有重要的科学意义与应用价值。本项目在前期研究基础上，采用玻璃分相技术制备纳米多孔石英玻璃棒，研究多孔玻璃中纳米级孔道对稀土离子的吸附，热成键及扩散的动态过程及机理。采用多次掺杂技术提高稀土离子掺杂浓度，研究团簇模型以及团簇抑制手段。制备基于纳米多孔石英玻璃的高掺杂石英光纤，研究不同结构和折射率剖面的高掺杂石英光纤的窄线宽激光特性。本项目的开展，将有助于发展基于玻璃分相技术的高掺杂石英光纤制备新技术，为高掺杂石英光纤提供新的理论指导和技术手段，为石英基窄线宽光纤激光器提供新的技术路线。

在高功率光纤激光器与光纤放大器中，受激布里渊散射与受激拉曼散射是限制功率提升的主要非线性效应，缩短掺杂光纤长度是抑制非线性效应的有效手段。基于玻璃分相技术，介绍了高掺杂光纤的制备过程。通过不断优化掺杂浓度、比例，实现大尺寸(Ф3*300mm)掺Yb3+石英玻璃芯棒的制备，进而制备大芯径(80/400μm)掺Yb3+双包层光纤。该光纤Yb3+的掺杂浓度为12200wt-ppm，在976nm处的吸收为6.5dB/m。基于MOPA结构，光纤长度仅2.5m时，其斜率效率达到79.5%，最大激光输出功率为600W，是目前国产基于玻璃分相技术最高输出功率。对于单纵模窄线宽超短腔光纤激光器，光纤的使用长度影响着谐振腔长，需要尽可能的减少所用掺杂光纤长度。基于改进的化学气相沉积工艺(MCVD)，通过引入共掺Al3+及P5+，制备了154.4dB/m吸收的超高浓度掺铒光纤，其团簇率仅为3.606%。使用的光纤长度为65cm，对于总功率0dBm的C波段信号，20dB增益带宽1528-1564nm，噪声系数小于5dB。这是目前国产最高浓度的掺杂铒纤。浓度猝灭是影响高浓度掺铒光纤性能的重要因素，项目研究了共掺离子和团簇的关系及抑制手段。Al3+与P5+结合形成的[AlPO4]四面体可以有效抑制Er3+的成对效应，降低团簇率。结果表明，较短的高浓度掺铒光纤可以为光通信系统提供足够的增益。研究结果表明高掺杂石英光纤在窄线宽激光器方面具有重要的应用前景。