低NA掺Yb大模场光纤的制备及激光性能研究

With the enhancing of fiber laser power, single mode output large mode field optical fiber become one of the important research hot spot and the main development direction. with the development of laser beam combining technology,10KW and even 100 kw high birightness laser power can be achieved. However, Limited by traditional low SBS threshold of rare earth doped quartz substrate, 3 KW single frequency Narrow spectral lines laser still can not breakthrough. In addition, both the higher core NA and also the mode instalbility become one of the important drawbacks in fiber laser.Exploring the regulation of ytterbium doped fiber core material SBS gain performance and obtain high SBS threshold of the fiber core matrix, so that much more higher narrow line width laser power can be obtained. In this topic, base on the MCVD techonology, we develope new rareearth ions liquid doping method by sol-gel technique.According to the uniform sol codoped with Y/Al/P/F/Mg/Ca the local envirionment of rareearth ions can be controled. on the one hand the SBS treshold can be increased due to the addition of Y2O3 in the core, on the ohter hand, the thermal optical coefficient can be balanced by Mg/Ca. In combination with the effect control by codoping F, the low NA larege mode area Yb doped fiber with higher SBS threshold can be preprared.

随着光纤激光功率的提升，可实现单模输出的大模场光纤成为重要的研究热点和主要发展方向。利用光纤激光的光谱合成技术可以实现10KW甚至100KW量级的高亮度激光输出。然而受限于传统稀土掺杂石英基质的低SBS阈值影响，利用单路光纤很难突破3KW功率的窄谱线激光输出。同时，由于纤芯数值孔径偏大以及热引起的模式不稳定也成为制约光纤激光亮度的重要因素。探索调控掺镱纤芯材料的SBS增益性能，获得高SBS阈值的纤芯基质，则有望进一步提升单频或窄谱线激光的功率水平。本课题提出基于MCVD工艺，开展稀土掺杂硅溶胶的浸泡掺杂工艺新思路，利用溶胶制备所实现的稀土离子的高分散性特点，通过共掺杂Y/Al/P/F/Mg/Ca等成分，实现稀土离子的微观局域环境调控，一方面降低纤芯的SBS增益系数，另一方面平衡纤芯的热光系数，同时利用高掺氟实现纤芯折射率的有效控制，最终制备得到高SBS阈值的低数值孔径掺镱大模场光纤。

针对现有稀土有源光纤面临的因稀土掺杂不均匀引起的增益均匀性差、非线性SBS效应带来的光谱展宽以及稀土离子团簇为重要原因的光暗化效应等几大限制窄线宽光纤激光功率的因素，探索研究一种基于MCVD工艺液相浸泡稀土掺杂二氧化硅纳米溶胶制备大模场光纤的技术。基于该课题，系统开展了优化、提高MCVD制备掺镱双包层光纤预制棒的工艺重复性和可靠性研究。从掺镱大模场光纤制备的全流程开展基础和关键关键技术攻关，提高掺镱大模场光纤的技术水平；研究了结构弛豫对 Al3+/Yb3+共掺石英玻璃结构和性能的影响规律；开展了Yb3+掺杂石英玻璃及光纤的温度特性研究；参考MCVD结合溶胶液相稀土掺杂工艺技术，采用毛细管进行管内溶胶凝胶镀膜工艺技术，创新发展稀土高掺石英基复合玻璃光纤制备技术。. 基于本课题研究，改进完善低数值孔径掺镱双包层光纤的制备技术，通过调控磷铝比实现AlPO4结构基团的形成，进一步共掺杂氟，成功制备了稀土掺杂浓度超过7500ppm的25/400及35/250型掺镱大模场双包层光纤，纤芯NA小于0.045，远低于Nufern公司的常规0.065NA，表明在制备低NA光纤方面，工艺技术已取得较大进展。进一步与用户对接，适当调控纤芯数值孔径和吸收系数，制备成功纤芯数值孔径为0.058的25/400型掺镱双包层光纤，实现了2.2kW的高效窄线宽激光放大，线宽为25GHz,光束质量因子M2约为1.2，处于国内先进水平。基于该成果，承担研制的低数值孔径的掺镱大模场光纤已逐步产品化并在其他课题中获得应用。另外，该课题研究的低数值孔径光纤，进一步对预制棒进行抗辐照加固工艺处理，还可以制备耐辐照掺镱光纤，从而为天基光纤激光器研制提供关键光纤材料。