An Optical Time Domain Reflectometer (OTDR) is the most powerful tool for characterizing fiber optic networks. It works like "radar for fiber optics," sending light pulses down the fiber and analyzing the reflected light to measure loss, locate faults, and verify installations. OTDR testing analyzes fiber optic cable performance from end to end by testing components along the cable, including connection points, bends, and splices. The measurement is said to be unidirectional as the. An OLTS provides the most accurate insertion loss measurement on a link by using a light source on one end and a power meter at the other to measure precisely how much light is coming out at the opposite end.