The optical time domain reflectometer (OTDR) is usually used for locating abnormal attenuation points on the optical line. the OTDR is used to test parameters such as the optical fiber length/attenuation/break, curve, return loss, fusion splicing loss, and reflection ratio of. The Optical Time Domain Reflectometer (OTDR) is useful for testing the integrity of fiber optic cables. It can verify splice loss, measure length and find faults. Later, comparisons can be made. An OTDR allows you to locate splices, faults and breaks in optical fiber by analyzing backscattered light.