Polarization dependence of Brillouin linewidth and peak frequency due to fiber inhomogeneity in single mode fiber and its impact on distributed fiber Brillouin sensing.
Polarization dependence of Brillouin linewidth and peak frequency due to fiber inhomogeneity in single mode fiber and its impact on distributed fiber Brillouin sensing.
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DOI：
10.1364/oe.20.006385
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发表时间：
2012-03
期刊：
影响因子：
3.8
通讯作者：
S. Xie;M. Pang;X. Bao;Liang Chen
中科院分区：
文献类型：
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作者：
S. Xie;M. Pang;X. Bao;Liang Chen
利用布里渊光时域分析（BOTDA）系统，研究了单模光纤（SMF）中由于光纤非均匀性引起的布里渊线宽和峰值频率与光波偏振态（SOP）的关系。理论分析表明，光纤的非均匀性导致光纤的双折射和声速的变化，这两个因素都会导致布里渊增益谱的展宽和不对称性，从而导致布里渊线宽和峰值频率随光波偏振态的变化。由于光纤在横向和纵向上的不均匀性，所测量的BGS是相互作用长度内具有不同峰值频率的几个频谱分量的叠加。当泵浦或探测SOP改变时，确定每个光谱分量的峰值效率的峰值布里渊增益和光学和声学模式轮廓的重叠区域在相互作用长度内变化，这进一步改变了叠加的BGS的线宽和峰值频率。在标准阶跃型SMF-28光纤上，通过BOTDA系统分别测量谱线不对称因子和拟合得到有效峰值频率，实验验证了布里渊线宽和峰值频率对SOP的依赖性。实验结果表明，在该光纤上，当探针输入为正交SOP时，布里渊频谱不对称因子和有效峰值频率随距离的变化范围分别为2%和0.06MHz。实验结果还表明，在分布式光纤布里渊传感中，扰偏器（PS）可以减小光纤横向不均匀性对布里渊线宽和峰值频率的SOP依赖性，但保持了光纤纵向不均匀性的影响。在非理想偏振置乱情况下，光纤非均匀性引起的有效布里渊峰值频率的波动是分布式光纤布里渊传感器传感频率分辨率的另一个限制。
The dependence of Brillouin linewidth and peak frequency on lightwave state of polarization (SOP) due to fiber inhomogeneity in single mode fiber (SMF) is investigated by using Brillouin optical time domain analysis (BOTDA) system. Theoretical analysis shows fiber inhomogeneity leads to fiber birefringence and sound velocity variation, both of which can cause the broadening and asymmetry of the Brillouin gain spectrum (BGS) and thus contribute to the variation of Brillouin linewidth and peak frequency with lightwave SOP. Due to fiber inhomogeneity both in lateral profile and longitudinal direction, the measured BGS is the superposition of several spectrum components with different peak frequencies within the interaction length. When pump or probe SOP changes, both the peak Brillouin gain and the overlapping area of the optical and acoustic mode profile that determine the peak efficiency of each spectrum component vary within the interaction length, which further changes the linewidth and peak frequency of the superimposed BGS. The SOP dependence of Brillouin linewidth and peak frequency was experimentally demonstrated and quantified by measuring the spectrum asymmetric factor and fitting obtained effective peak frequency respectively via BOTDA system on standard step-index SMF-28 fiber. Experimental results show that on this fiber the Brillouin spectrum asymmetric factor and effective peak frequency vary in the range of 2% and 0.06MHz respectively over distance with orthogonal probe input SOPs. Experimental results also show that in distributed fiber Brillouin sensing, polarization scrambler (PS) can be used to reduce the SOP dependence of Brillouin linewidth and peak frequency caused by fiber inhomogeneity in lateral profile, however it maintains the effects caused by fiber inhomogeneity in longitudinal direction. In the case of non-ideal polarization scrambling using practical PS, the fluctuation of effective Brillouin peak frequency caused by fiber inhomogeneity provides another limit of sensing frequency resolution of distributed fiber Brillouin sensor.