Influence of Refractive Index Distribution on Brillouin Gain Spectrum in GeO_(2)-Doped Optical Fibers

二氧化锗掺杂光纤中折射率分布对布里渊增益谱的影响

GeO_(2) is commonly used as dopant to adjust the refractive index profile(RIP)and the acoustic velocity profile(AVP)in the fiber,thereby forming different Brillouin gain spectrum(BGS)characteristics such as Brillouin gain,acoustic mode number and peak intensity difference.When an optical fiber is used in optical fiber sensing or communication system,its BGS characteristics may play an important role in determining the performance of the system.In this paper,finite element analysis(FEA)method is used to study the influence of refractive index distribution and its corresponding AVP on the BGS in step-index,graded-index,and complex-index optical fibers.A new method has also been proposed to efficiently discriminate acoustic mode solution and obtain the new and full images of total Brillouin gain and acoustic modes number of the fiber as a function of the refractive index distribution,considering the influence of changing the refractive index difference and the geometric size simultaneously.For each type of optical fiber,the recommended parameter range is provided for optical fiber sensing and optical fiber communication.Moreover,the suitable optical fiber with close peak intensity in its multi-peak BGS is explored and achieved,which can be used in Brillouin beat spectrum detection systems to improve sensing accuracy.

二氧化锗通常用作掺杂剂来调控光纤中的折射率分布(Refractive index profile,RIP)和声速分布(Acoustic velocity profile,AVP),从而在光纤中形成不同的布里渊增益谱(Brillouin gain spectrum,BGS)特性,如布里渊增益、声模式数和峰强度差。当光纤用于光纤传感或光纤通信系统时,其BGS特性可能在确定系统性能方面起重要作用。本文通过有限元分析法(Finite element analysis,FEA)研究阶跃折射率光纤、渐变光纤以及复杂折射率分布光纤中RIP及相应的AVP对布里渊增益谱的影响。提出了一种新的方法,可以有效分辨出声模式解,同时改变光纤折射率分布与几何尺寸,获得光纤总布里渊增益和声模式数同折射率分布关系的新的完整图像。对于每一类光纤,提供了用于光纤传感与光纤通信的建议参数。探索并找到了具有相近布里渊峰强度的多峰布里渊增益谱的光纤,该光纤能够用于布里渊拍频谱检测并提高传感精度。