Bismuth-doped fibre laser systems

在过去的十年中，高功率光纤激光器的研究和开发取得了如此迅速的进展，这些设备正在成为实验室或工业工作场所中许多新的和传统应用的首选激光器，从生物成像到钢板的切割和焊接。这些进步得到了科学和技术的几个主要贡献的加强，如多包层光纤结构，可靠的高功率单条泵浦二极管和独特的多模光纤耦合器在泵浦技术。迄今为止，最先进的光纤激光器技术依赖于传统硅基光纤的稀土离子掺杂。硅基纤维的使用允许易于处理，以及与现有纤维技术的兼容性和集成。Yb、Yb：Er和Tm的稀土离子主要覆盖三个主要波长区域，分别在1030-1120 nm、1530-1600 nm和1750-2100 nm附近工作。因此，在1000-2000 nm的光谱范围内存在这些掺杂光纤激光器不能工作的非常显著的间隙。这可以通过光纤拉曼激光器技术来解决，然而，到超高平均功率水平的可缩放性是有问题的，能量存储因此脉冲能量是特别的问题，因为受激拉曼激光器在受激散射过程中利用虚拟状态，而有效操作所需的长光纤长度中的附加非线性意味着激光器的线宽被加宽，阻碍了倍频，特别是黄色和橙子中的重要波长。此外，尽管拉曼器件已经取得了巨大的成就，但在第二通信窗口中，在1300 nm左右的石英光纤的最小色散区域，还没有传统的稀土掺杂石英光纤激光器或光纤放大器。最近，我们在IRCICA-PHLAM（里尔大学）的合作者已经生产出了新的掺铋石英光纤。这些纤维表现出非常宽的发光轮廓，从约1000 nm延伸到1600 nm。在这个项目中，我们计划分析和研究连续激光和功率缩放的全光纤集成格式的掺铋激光器，方便地泵浦Yb光纤激光器。此外，将研究可调谐激光器方案，以及线窄化机制和倍频输出到黄橙色光谱区应该是可以实现的，在可见光的平均功率在瓦特级。在这些波长和功率水平下的紧凑型激光系统应该与眼科治疗以及美容手术中的应用相关。除了允许广泛的可调谐性之外，宽增益带宽还允许支持超短脉冲，我们将基于这种独特的材料开发皮秒和飞秒光纤激光器。在1050 nm和1300 nm附近的宽带ASE操作也可以与光学相干层析应用相关。掺Bi石英光纤的增益峰值在单模石英光纤的最小色散区域1270 nm。因此，在该光谱范围内存在开发极宽带宽电信相关光纤放大器的潜力。可以看出，Bi掺杂的石英光纤首次提供了扩大掺杂光纤技术在上述无法达到的光谱区域中的作用的机会，并且应该进一步加强这些不可或缺的设备的科学和技术发展。

Over the past decade such rapid progress has been made on the research and development of high power fibre lasers that these devices are becoming the laser of choice in numerous new and traditional applications in the laboratory or the industrial work place, from biological imaging to the cutting and welding of steel plates. These advances have been enhanced by several major contributions to the science and technology such as multiclad fibre structures, reliable high power single stripe pump diodes and unique multimode fibre couplers in pumping technology. To date, the most advanced fibre laser technologies have relied upon rare earth ion doping of conventional silica based fibres. The use of silica based fibres allows ease of handling, as well as compatibility and integration with existing fibre technology. Primarily three principal wavelength regions are covered by the rare earth ions of Yb, Yb:Er and Tm, operating broadly around 1030-1120 nm, 1530-1600 nm and 1750-2100 nm, respectively. Consequently, there are very significant gaps in the spectral range 1000-2000 nm where these doped fibre lasers cannot operate. This can be solved by fibre Raman laser technology, however, scalability to ultra high average power levels is problematic, energy storage hence pulse energy is a particular problem because the stimulated Raman laser utilizes a virtual state in the stimulated scattering process, while additional nonlinearity in the long lengths of fibre necessary for efficient operation means that the linewidths of the lasers are broadened impeding frequency doubling, in particular to important wavelengths in the yellow and orange. In addition, despite the impact Raman devices have made, no conventional rare earth doped silica based fibre laser or fibre amplifier is available in the second telecom window in the region of minimum dispersion of silica based fibres around 1300nm.This basic-research project will address these issues. Recently, our collaborators at IRCICA-PHLAM (Lille University) have produced new Bismuth-doped silica fibres. These fibres exhibit an extremely broad luminescence profile, extending from about 1000nm to 1600nm. In this project we plan to analyse and investigate cw lasing and power scaling of fully fibre integrated formats of the Bi-doped laser, conveniently pumped by Yb fibre lasers. In addition, tunable laser schemes will be investigated as well as line narrowing mechanisms and frequency doubling of the output to the yellow-orange spectral region should be achievable, with average powers in the visible at the watt level. Compact laser systems at these wavelengths and power levels should be of relevance to applications in ophthalmic treatments as well as in cosmetic surgery. The broad gain bandwidth in addition to allowing extensive tunability should also permit the support of ultrashort pulses and we will develop both picosecond and femtosecond fibre lasers based upon this unique material. Broadband ASE operation around 1050nm and 1300nm can be also of relevance to optical coherence tomograpfy applications.The peak of the gain in Bi-doped silica fibre is in the range of 1270 nm, the region of minimum dispersion of single mode silica fibre. Consequently, the potential exists for the development of an extremely broad bandwidth telecommunications relevant fibre amplifier in this spectral range. It can be seen that Bi-doped silica fibre presents for the first time the opportunity to expand the role of the doped fibre technology in unattainable spectral regions as described above and should further enhance the scientific and technological development of these indispensable devices.