Opt Lett. 2023 Jul 1;48(13):3603-3606. doi: 10.1364/OL.493139.
Femtosecond inscription of fiber Bragg gratings (FBGs) in each core of a cladding-pumped seven-core Yb-doped fiber enables efficient (≈70%) 1064-nm lasing in a robust all-fiber scheme with ≈33 W power, nearly the same for uncoupled and coupled cores. However, the output spectrum is quite different: without coupling, seven individual lines corresponding to the in-core FBG reflection spectra sum up into a broad (0.22 nm) total spectrum, whereas the multiline spectrum collapses into a single narrow line at strong coupling. The developed model shows that the coupled-core laser generates coherent superposition of supermodes at the wavelength corresponding to the geometric mean of the individual FBG spectra, whereas the generated laser line broadens, with a power (0.04-0.12 nm) like the single-core mode of a seven-times larger effective area.
飞秒激光在包层泵浦七芯掺镱光纤的每个纤芯中写入光纤布拉格光栅（FBG），在具有约 33W 功率的稳健全光纤方案中实现了高效（约 70%）的 1064nm 激光，对于非耦合和耦合纤芯而言，功率几乎相同。然而，输出光谱却大不相同：没有耦合时，七个对应纤芯 FBG 反射光谱的单独线叠加成一个宽（0.22nm）的总光谱，而在强耦合时，多线光谱则坍塌成一个单一的窄线。所开发的模型表明，耦合纤芯激光在与单个 FBG 光谱的几何平均值对应的波长处产生超模的相干叠加，而生成的激光线变宽，其功率（0.04-0.12nm）与有效面积大七倍的单芯模式相同。
