Li Huizi, Goel Charu, Zang Jichao, Raghuraman Sidharthan, Chen Shaoxiang, Abu Hassan Muhammad Rosdi, Chang Wonkeun, Yoo Seongwoo
Opt Express. 2022 Feb 28;30(5):7928-7937. doi: 10.1364/OE.451033.
We proposed and demonstrated mode cleaning in a high-power fiber laser by integrating an anti-resonant hollow-core fiber (AR-HCF) into a multimode laser cavity of an ytterbium (Yb)-doped fiber (YDF). An in-house mode-matched AR-HCF was fusion-spliced to a commercial multimode LMA-YDF, ensuring efficient fundamental mode coupling. The AR-HCF inflicts a high propagation loss selectively on higher-order modes, facilitating fundamental mode operation. Thus, the AR-HCF works as an efficient spatial mode filter embedded in the multimode fiber laser cavity and reinforces preferential amplification of the fundamental mode. Beam quality factor enhancement was achieved from M = 2.09 to 1.39 at an output power of 57.7 W (pump-power limited). The beam quality can be further improved by refining the AR-HCF fabrication. The proposed technique has a great potential to be exploited in other multimode fiber laser cavities involving erbium- or thulium-doped fibers and obviates the need for complicated specialty active fiber designs. Compared with the commonly used fiber bending technique, our method can achieve an efficient higher-order mode suppression without inducing mode-field deterioration.
我们通过将反谐振空芯光纤（AR-HCF）集成到掺镱（Yb）光纤（YDF）的多模激光腔中，提出并展示了高功率光纤激光器中的模式清洁。将内部模式匹配的AR-HCF熔接至商用多模大模场面积YDF，确保了高效的基模耦合。AR-HCF对高阶模选择性地施加高传输损耗，有利于基模运转。因此，AR-HCF作为嵌入多模光纤激光腔中的高效空间模式滤波器，增强了基模的优先放大。在57.7 W的输出功率（受泵浦功率限制）下，光束质量因子从M = 2.09提高到了1.39。通过优化AR-HCF的制造工艺，光束质量可进一步提高。所提出的技术在涉及掺铒或掺铥光纤的其他多模光纤激光腔中具有很大的应用潜力，并且无需复杂的特种有源光纤设计。与常用的光纤弯曲技术相比，我们的方法能够在不引起模场劣化的情况下实现高效的高阶模抑制。
