Fiber Optics: Decoding the OTDR Trace

In FTTH networks, the OTDR (Optical Time-Domain Reflectometer) is one of the most powerful tools we use in the field. It doesn't only measure distance it helps us understand what's really happening inside the fiber. An OTDR (Optical Time-Domain Reflectometer) is a high-tech "fiber radar" used to test the health of fiber optic cables. It doesn't just check if a signal is passing through; it creates a visual map (a trace) of the entire cable, showing exactly where every splice, connector, and fault is located.

Purpose of an OTDR

Essentially, an Optical Time Domain Reflectometer (OTDR) acts like a high-tech radar for fiber optic cables. Its main job is to check for insertion loss—basically seeing how much signal strength is lost from one end of the cable to the other—by measuring how light scatters as it travels.

Beyond just measuring loss, the OTDR identifies specific "events" along the line, such as connectors or splices, by measuring their reflectance. This tells you how much light is bouncing back toward the source; a "higher" number (one closer to 0 dB) usually signals a problem like a dirty or damaged connection. While reflectance is recorded as a negative value, its counterpart, return loss, is expressed as a positive number. In both cases, the further the value is from zero, the better your cable is performing.