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. VIAVI Solutions explains the basics: “An OTDR contains a laser diode as a light source, a photodiode as a detector and a precise time base. The laser emits a pulse of light at a specific wavelength that propagates through the optical fiber to be tested. All are written in the same straightforward format: what equipment do you need, what are the procedures for testing, options in implementing the test, measurement errors and documenting the results.