OTDRs inject high-powered light pulses into the fiber using specialized laser diodes. If the pigtail is sufficiently long, 10 meters or so, VIAVI SolutionsTM Optical Time Domain Reflectometers (OTDRs) with pulses as short as 1 foot can perform these measurements. What Is an OTDR? What Is an OTDR? An OTDR is a powerful tool that helps technicians and engineers assess the health of fiber optic cables. This test will acquire a trace of an installed fiber optic cable plant, singlemode or multimode, including the loss of all fiber, splices and connectors. The method shown is on the FOA "1 Page Standard" FOA4 which you may print or download and insert in your documentation.