研究了椭圆纤芯少模光纤的模式特性,给出了少模光纤中克尔非线性耦合模方程的一般形式,详细描述了少模光纤参量放大器的设计方法。利用COMSOL仿真软件获得了导波光场模式分布对纤芯椭圆率的依赖关系,进而计算了少模之间的四波混频相位失配因子和相应的模场交叠积分(或非线性系数)。研究了阶跃型折射率分布的椭圆纤芯少模光纤中三个模群的简并四波混频过程。结果表明,当LP_21a模的抽运光功率为0.5 W时,LP_11a模的信号光增益达到20.15 dB,在增益劣化2 dB的范围内可允许的椭圆纤芯误差为0.6 μm。

Herein, we studied the mode characteristics of a few-mode fiber with an elliptical-core. We investigated the general expression of the Kerr nonlinear coupled-mode equations for the few-mode fiber and discussed the design process of an optical fiber parametric amplifier in detail. The dependence of the optical field mode distribution on core ellipticity was simulated using the COMSOL software, following which the phase mismatch factor in four-wave mixing and the corresponding mode field overlapping integral (or nonlinear coefficient) were calculated. In addition, we studied the degenerate four-wave mixing process of three mode groups in the elliptical-core few-mode fiber with a step refractive index distribution. The results show that when the LP21a-mode pump power is 0.5 W, the maximum gain of 20.15 dB can be obtained and the elliptical-core tolerance size is 0.6 μm in the gain deterioration range of 2 dB.