由于探测光脉冲宽度受到限制,布里渊光时域反射仪(BOTDR)在对光纤上的应变进行分布式测量时,空间分辨力只能达到1 m。针对布里渊光时域反射仪单次采样接收背向布里渊散射信号(BBS)需要一定的时间,提出了基于等效脉冲光的多洛仑兹拟合法以提高其应变测量的空间分辨力。该方法将探测光脉冲在布里渊光时域反射仪完成单次采样所需的时间上进行积分,将积分函数作为等效脉冲光的表达式,再根据等效脉冲光的形状将布里渊光时域反射仪接收到的背向布里渊散射谱(BBS)细分,并对它进行多洛仑兹迭代拟合,准确求得每个细分布里渊散射谱的中心频率,进而利用光纤中布里渊频移与应变的对应关系,得到光纤中与细分布里渊散射谱对应的细分光纤单元上的应变情况。实验结果表明,利用这种方法,可使布里渊光时域反射仪应变测量的空间分辨力提高至0.05 m。

Brillouin optical time-domain reflectometer (BOTDR) can perform distributed strain measurement along an optical fiber. Its highest spatial resolution is limited to 1 m because of the restricted probe pulse width. Because the time to accomplish one single sampling by BOTDR cannot be neglected compared to probe optical pulse width, a novel multi-Lorentz fitting method based on equivalent optical pulse (EOP) is proposed to improve its spatial resolution. In this method, the equivalent optical pulse is obtained by integrating the probe optical pulse over the time to accomplish one single sampling by BOTDR and the backscattered Brillouin signal (BBS) received by BOTDR is decomposed into sub-BBSs according to the shape of equivalent optical pulse. Then the backscattered Brillouin signal is fitted by multi-Lorentz function to obtain central frequency of each sub-BBS. The strain in the length corresponding to each sub-backscattered Brillouin signal can be obtained by use of the dependence of Brillouin frequency shift on strain. It is experimentally demonstrated that the spatial resolution for strain measurement with BOTDR is improved to 0.05m by the proposed method.