optical time-domain reflectometry
In optical fiber communications, the losses in optical fibers can be measured with optical time domain reflectometers. The measuring method works similar to radar but works with very low light levels and helps to localize poor fiber splices or faulty optical components.
In Optical Time Domain Reflectometry a fast light pulse is injected into the measured system (for example a fiber optic line). OTDR measurements are similar to TDR measurements, but are based on emitting a series of light pulses, e.g. by means of a laser. Here, the time of the reflections is determined from the reflection loss by measuring from the same end of the fiber how much light passes over the Rayleigh backscatter or is being reflected from individual locations along the fiber. OTDR measurement technology provides a snapshot of the entire connectivity of fiber optic networks, including all link points, splices, and fiber sections.
With help of a fast ADCs or TDCs the time parameters of the reflections and scatterings are measured in order to determine the location of the fault.
Please also read our detailed article on this topic.