随着人类社会对光纤通信网络的依赖程度越来越高，实时诊断和定位光纤通信网络中的工作故障点，以保证系统的正常工作一直是光纤通信领域研究的热点问题。到目前为止，较昂贵的光时域反射仪（OTDR）一直是诊断光纤链路故障点的主要工具。然而，由于测量原理上的局限，传统的OTDR无法应用于较复杂的光网络环境，只适合点到点的传输链路，且无法实现在线实时测量。 本项目提出了一种低成本的、可在线诊断WDM-PON网络中光纤故障点的新方法。光网络中的通信信号和它在光纤中传输时产生的后向瑞利散射信号具有δ函数型的相关曲线。曲线上峰值的位置和大小均携带着光纤反射点的信息。本方法利用通信信号自身作为参考光和探测光，结合相关探测法，通过检测参考光和瑞利散射光的互相关曲线，进而诊断、定位光纤链路中的故障点。此方法成本低廉，不但可同时实现高分辨率、大动态范围的在线测量，而且还可以实现多个波长信道中光纤故障点的同时诊断。

With people's dependence on optical fiber communication network increased, real-time diagnosis and location of fiber fault in optical network has been the hot topics in optical fiber communication field. So far, the expensive Optical time domain reflectometer(OTDR) has always been the primary tool of the fiber fault diagnosis. However, due to the theoretical limitations, the conventional OTDR technique cannot be applied to much more complex optical network, but only to point-to-point fiber link. This project propose a cost-effetive method that be able to real-time measure and locate fiber faults in WDM-PON. The cross-correlation trace of the signals in the optical network and their backward Rayleigh scattering lights exhibits a characteristic"δfunction-like". The level and location of the peaks of the cross-correlation trace carry the information about the fiber faults.By using communication signals themselves as reference and detecting lights and correlation-detection technique, this low-cost method is not only to enable us to real-time diagnose and locate the fiber faults of WDM-PON with high spatial resolution and high dynamic range, but also to realize simultanoues diagnosis of fiber faults in multi-channels.