Abstract: Various embodiments of an apparatus for measuring a length of an optical fiber are provided. In one embodiment, a method of testing an optical fiber comprises measuring a length of the optical fiber based on a time of flight of an optical pulse launched through the optical fiber from a first optical time domain reflectometer (OTDR) system and received by a second OTDR system; and controlling the first and the second OTDR systems to characterize the optical fiber based on the measured length of the optical fiber. In this way, defects and other physical characteristics of an optical fiber may be accurately determined.