In order to reduce the problem of inter-mode crosstalk in the low-mode fiber, a new type of dual coupling ring assisted few-mode fiber structure design is proposed, the main influencing factors of crosstalk in the 6-LP mode are analyzed, and five main structural parameters of the new dual coupling ring structure are simulated and analyzed. Based on this designed structure, a 6-LP few-mode fiber is developed, which reduces the inter-mode crosstalk in the few-mode fiber. The results show that in the 6-LP few-mode fiber, the effective mode refractive index difference between the LP21 mode and the LP02 mode is the closest, and the difference is the main factor affecting crosstalk. The double coupling ring structure adjusts the effective mode refractive indices of the LP21 mode and the LP02 mode. In this structure, the minimum refractive index difference between LP21 and LP02 is 1.5×10-3, which is 1.88 times the minimum refractive index difference of the traditional step structure under the same conditions.
Hongfei Zang, Feng Tian, Yongjun Wang. Design of Low Crosstalk Double Coupling Ring Assisted 6-LP Fiber[J]. Chinese Journal of Lasers, 2022, 49(3): 0306002