Jiang Chen, Zhou Kaiming, Sun Bing, Wang Zhiqiang, Wan Ying, Ma Yuehui, Mou Chengbo, Shen Lei, Zhang Lei, Luo Jie, Liu Yunqi
Opt Lett. 2022 Jul 1;47(13):3207-3210. doi: 10.1364/OL.461547.
We propose and demonstrate the inscription of parallel long-period gratings (LPGs) in a few-mode fiber (FMF) using femtosecond lasers. Mode conversion from the fundamental (LP) mode to high-order core modes, including LP, LP, LP, LP, and LP, is achieved by controlling the inscription period of the gratings. Taking advantage of the highly focused femtosecond laser, LPGs with different off-axis offsets were fabricated, and the resonance wavelength and the inscription efficiency of the gratings versus the offset were investigated. Based on the off-axis writing technique and using the femtosecond laser source, we wrote parallel LPGs that contain multi-gratings in a single FMF and achieved a multi-channel core mode converter in a single FMF with flexibility in terms of the resonant wavelength and mode conversion among different modes. This approach offers a new, to the best of our knowledge, option for implementation with high integration, and a multi-channel mode converter, which could find potential applications in FMF multi-wavelength laser systems, and wavelength/mode division multiplex communication systems. Furthermore, these microstructured LPGs integrated into an optical fiber can be used as a multifunctional sensor.
我们提出并演示了使用飞秒激光在少模光纤（FMF）中写入平行长周期光栅（LPG）。通过控制光栅的写入周期，实现了从基模（LP）到高阶纤芯模式（包括LP、LP、LP、LP和LP）的模式转换。利用高度聚焦的飞秒激光，制作了具有不同离轴偏移的LPG，并研究了光栅的共振波长和写入效率与偏移的关系。基于离轴写入技术并使用飞秒激光源，我们在单根FMF中写入了包含多个光栅的平行LPG，并在单根FMF中实现了多通道纤芯模式转换器，在共振波长和不同模式间的模式转换方面具有灵活性。据我们所知，这种方法为高集成度实现提供了一种新的选择，以及一种多通道模式转换器，其可能在FMF多波长激光系统和波长/模式分复用通信系统中找到潜在应用。此外，这些集成到光纤中的微结构LPG可用作多功能传感器。
