Optimization Of Bend-insensitive Few-mode Fibers

With the rapidly increase of data traffic and the capacity of transmission system, Mode Division Multiplexing (MDM) transmission using Few-mode Fibers(FMFs), which provides multi-channel multiplexing, high efficiency of frequency spectrum and low nonlinear effects, has been attracted as new generation optical fiber communication systems in order to realize large transmission capacity.In this paper, a general formula of bending loss based on perturbation theory is derived and verified by finite element method. The fundamental mode LPoi and the following high-order modes i. e. LP11, LP21 and LP02 modes and the parameters (the distance of core-trench, the width of trench, the refractive index difference of trench-cladding and core radius) of SIFMF and PPFMF structure are considered to study the bending performance. Then, we present a novel design strategy of few-mode trench-assisted bend-insensitive fibers (FM-TA-BIFs) based on the particle swarm optimization (PSO). It is found that, in the structure parameters of trench-assisted FMF, with the cutoff wavelength and bending radius fixed the bending loss of each mode of FMFs increase with the increasing of fiber radius. An optimized distance between trench and core for each high-order mode is also investigated for obtaining minimum bending losses, which plays an important role in controlling the bending performance of FMFs. There is a trade-off between bending loss and effective mode field area, so we defined PI as the ratio of bending loss and effective mode field. An optimization design method based on the PSO has been applied for SIFMF and PPFMF to find the optimal parameters of fiber. The conclusions are of significance for the design and manufacture of bend-insensitive few-mode fibers.