Opt Express. 2023 Mar 13;31(6):10007-10018. doi: 10.1364/OE.484504.
By increasing the number of modes of transmission in optical fiber, the mode-division multiplexing (MDM) technology can effectively improve the transmission capacity. The mode add-drop technology is an important part of the MDM system and a key element for realizing flexible networking. In this paper, a mode add-drop technology based on few-mode fiber Bragg grating (FM-FBG) is reported for the first time. The technology utilizes the reflection characteristics of Bragg grating to realize the add-drop function in the MDM system. The grating is written in parallel according to the optical field distribution characteristics of different modes. By changing the writing grating spacing Δa to match the optical field energy distribution of the few-mode fiber, the few-mode fiber grating with high self-coupling reflectivity for the high-order mode is fabricated, and the performance of the add-drop technology is improved. The mode add-drop technology is verified in a 3 x 3 MDM system, which uses quadrature phase shift keying (QPSK) modulation and coherence detection. The experimental results show that the excellent transmission, add, and drop of 3 x 8 Gbit/s QPSK signals in 8 km few-mode fibers are achieved. The realization of this mode add-drop technology only requires Bragg gratings, few-mode fiber circulators, and optical couplers. It has the advantages of high performance, simple structure, low cost, and easy implementation, and it can be widely used in the MDM system.
通过增加光纤中的传输模式数量，模式复用（MDM）技术可以有效地提高传输容量。模式分插技术是 MDM 系统的重要组成部分，也是实现灵活组网的关键要素。本文首次报道了一种基于少模光纤布拉格光栅（FM-FBG）的模式分插技术。该技术利用布拉格光栅的反射特性，在 MDM 系统中实现分插功能。光栅根据不同模式的光场分布特性进行平行写入。通过改变写入光栅间距Δa，使其与少模光纤的光场能量分布相匹配，制作出具有高自耦合反射率的少模光纤光栅，从而提高分插技术的性能。在一个 3×3 的 MDM 系统中验证了模式分插技术，该系统采用正交相移键控（QPSK）调制和相干检测。实验结果表明，在 8km 少模光纤中实现了 3×8Gbit/s QPSK 信号的优异传输、分插。这种模式分插技术的实现仅需要布拉格光栅、少模光纤环行器和光耦合器。它具有性能高、结构简单、成本低、易于实现等优点，可广泛应用于 MDM 系统中。
