Opt Lett. 2019 Jan 15;44(2):279-282. doi: 10.1364/OL.44.000279.
The cascaded Raman fiber laser is a proven technology that provides wavelength agile high-power fiber lasers outside the rare-earth emission windows. However, conventional cascaded Raman fiber lasers lack wavelength agility due to the use of fixed wavelength fiber Bragg gratings. Recently, proposed cascaded Raman fiber lasers based on random distributed feedback have provided a grating-free solution enabling wavelength agility. With these lasers, wide wavelength tunability has been achieved. However, there are still limitations in scaling output power while maintaining high spectral purity of wavelength conversion. Spectral purity is characterized by the in-band power ratio, which is the ratio of the output power in the required wavelength to the total power. The origin of this limitation arises from the inability to efficiently terminate the Raman cascade at a specific wavelength with increasing power. In this Letter, we propose a novel filtered distributed feedback mechanism to terminate the Raman cascade at any desired wavelength, enabling power scaling with high spectral purity. Output power up to 28 W has been achieved with >85% in-band power ratio and >400 nm tuning range from 1118 to 1535 nm.
级联拉曼光纤激光器是一种成熟的技术，它在稀土发射窗口之外提供波长灵活的高功率光纤激光器。然而，由于使用固定波长光纤布拉格光栅，传统的级联拉曼光纤激光器缺乏波长灵活性。最近，提出了基于随机分布反馈的级联拉曼光纤激光器，它提供了一种无光栅的解决方案，实现了波长灵活性。利用这些激光器，已经实现了宽波长调谐。然而，在保持波长转换的高光谱纯度的同时，仍然存在限制输出功率的问题。光谱纯度的特点是带内功率比，它是所需波长的输出功率与总功率的比值。这种限制的根源在于，随着功率的增加，无法有效地在特定波长终止拉曼级联。在这封信件中，我们提出了一种新颖的滤波分布式反馈机制，可以在任何所需的波长终止拉曼级联，从而实现高光谱纯度的功率扩展。已经实现了高达 28 W 的输出功率，带内功率比>85%，波长调谐范围为 1118 到 1535nm，跨度超过 400nm。
