High Quality Content by WIKIPEDIA articles! In telecommunications, Return loss or Reflection loss is the reflection of signal power resulting from the insertion of a device in a transmission line or optical fiber. It is usually expressed as a ratio in dB relative to the transmitted signal power. Optical Return Loss is a positive number, historically ORL has also been referred to as a negative number. Within the industry expect to see ORL referred to variably as a positive or negative number. This ORL sign ambiguity can lead to confusion when referring to a circuit as having high or low return loss; so remember:- High Return Loss = lower reflected power = large ORL number = generally good. Low Return Loss = higher reflected power = small ORL number = generally bad.