Research On Low-Bending-Loss And Large-Mode-Area Fiber

Large-mode-area fibers can effectively solve the problem of nonlinear effect caused by the increase of optical power in the fiber.Therefore,it can make the fiber lasers have higher beam quality and reduce the physical damage caused by excessive light intensity in fibers.However,the bending loss usually increases with the increase of the effective mode area.Meanwhile,fiber lasers have developed rapidly,and they have tended to be miniaturized,integrated and compact for various complex scenarios,which puts forward higher requirements for the bending resistance of fibers.Therefore,it is of great significance to resolve the contradiction between large mode area and low bending loss.The main work of this paper is as follows:(1)A new quasi-37-core low-bending large-mode-area fiber based on the traditional19-core fiber is proposed in this paper,which has twenty air holes and seventeen cores.It can realize single-mode transmission or strict dual-mode transmission(fundamental mode HE₁₁ and second-order vector mode HE₂₁),the second-order vector modes TE₀₁ and TM₀₁are cut off by the air hole structure.Its mode field distribution,mode characteristics and bandwidth of single-mode and dual-mode is anlazyed.The effects of various structural parameters of the fiber on the effective refractive index and effective mode area are studied systematically.By adjusting the structural parameters,the fiber is controlled to be in single-mode transmission or strictly dual-mode transmission.In the case of maintaining strict dual-mode transmission,by optimizing the structural parameter,the effective area of the fundamental mode can be up to 1557.91?m².When the bending radius is 0.47 m,the effective area of the fundamental mode can be up to 1534.08?m²,while maintaining a low bending loss of less than 10^-3d B/m.The performance of this fiber is obviously better than that of traditional 19-core fiber.(2)In order to further improve the performance of the fiber and make its structure more stable,a trench-assisted quasi-19-core low-bending large-mode-area fiber is proposed in this paper.It is based on the quasi-37-core low bending large mode area fiber with a surrounding air hole replaced by a ring fluorine-doped trench with lower refractive index than the cladding,which reduces the number of air holes and makes the structure more stable.Again,its mode field distribution,mode characteristics and bandwidth of single-mode and dual-mode is anlazyed.The relationship between the structural parameters and the effective refractive index and effective mode area of the fiber is discussed in detail.In the case of maintaining strict dual-mode transmission,the effective area of the fundamental mode of the optimized fiber can be up to 2072.58?m².When the bending radius is 0.42 m,the effective area of the fundamental mode can be up to 2026.19?m²,and the bending loss is reduced to less than 10^-3 d B/m.The performance of this fiber is better than the new quasi-37 core fiber.The low-bending large-mode-area fibers proposed in this paper have important guiding significance for the transmission of high-power fiber lasers,amplifiers and large-capacity optical communication systems.