变纤芯直径传能光纤中受激拉曼散射传输特性的理论研究

Theoretical study on transmission characteristics of stimulated Raman scattering in passive fiber with variable core radius

锥形光纤纤芯直径沿着光纤长度方向均匀增大,在抑制非线性效应方面有着独特的优势。理论对比了单横模高斯光束输入时,输入纤芯直径均为50μm、纤芯直径沿着光纤长度方向恒定、线性增大和非线性增大的变纤芯直径传能光纤的输出光谱演化和拉曼光特性。在相同条件下,输入功率10 kW时,恒定型传能光纤的输出光谱中,拉曼抑制比(定义为输出光谱中信号光峰值强度分贝值与拉曼光峰值强度分贝值之差)为33.1 dB,线性增大和非线性增大型的输出拉曼抑制比分别为47.0,48.6 dB,分别优于恒定型传能光纤13.9,15.5 dB;输入功率达17.5 kW时,恒定型传能光纤中有81.6%的输入能量被耗散或转移到其他波长,线性增大和非线性增大型仅不到2%,其输出的信号光波段能量占总输入能量的98.1%,98.9%。结果表明,使用线性增大型或非线性增大型传能光纤代替恒定型常规光纤,可以有效提高受激拉曼散射阈值,相关研究可以为大功率光纤合束器和光纤端帽的设计提供有益参考。

Tapered fiber has unique advantages in suppressing nonlinear effects because its core radius increases uniformly along the length of the fiber.In this paper,the output spectrum evolution and Raman performance of three different types of passive fibers are simulated and analyzed under the input of single transverse mode Gaussian beam:the passive fibers with constant core radius,linearly increasing radius and nonlinearly increasing core radius,all have the same input core diameter of 50μm.Under the same conditions,when the input power is 10 kW,the Raman suppression ratio(defined as the difference between the intensity of the signal peak and the Raman peak in the spectrum)of constant type passive fiber is 33.1 dB,while those of the linear type and nonlinear type are 47.0 dB and 48.6 dB,respectively,which are better than that of constant type by 13.9 dB and 15.5 dB;When the input power reaches 17.5 kW,81.6%of the input energy of the constant type is dissipated or transferred to other wavelengths,while that of linear and nonlinear types is less than 2%,and the output signal optical band energy accounts for 98.1%and 98.9%of the total input energy.The results show that the threshold of stimulated Raman scattering can be effectively improved by using linear or nonlinear passive fiber instead of constant type,and the study can provide a useful reference for the design of high-power fiber combiner and fiber end cap.