光时域反射法（OTDR）Optical time domain reflection method (OTDR)基本原理：光源发出的光在沿光纤向前传输的过程中产生后向散射，后向散射光强在传播过程中随着距离增长而按一定规律衰减，在光速不变的情况下，距离与时间成正比。因此，根据探测器探测到的后向散射光强及其到达探测器的时间，就可以知道沿光纤路径上任一点的初始后向散射光强。Basic principle: the light emitted by the light source will generate backscattering in the process of forward transmission along the optical fiber, and the intensity of backscattered light will decrease in a certain rule as the distance increases in the process of backward propagation. Under the condition that the speed of light remains unchanged, the distance is proportional to time. Therefore, the initial backscattered light intensity at any point along the fiber path can be known based on the backscattered light intensity detected by the detector and the time it took to reach the detector.光的后向散射包括瑞利散射、喇曼散射和布里渊散射3种形式。The backscattering of light includes Rayleigh scattering, Raman scattering and brillouin scattering.