The most frequent cause of high reflectance is poor connector termination. This can occur due to dirty connectors, improper polishing, or poor splicing. This is always measured in dB (decibels) and will be displayed as a negative number. The closer the number is to. Reflectance (which has also been called "back reflection" or optical return loss) of a connection is the amount of light that is reflected back up the fiber toward the source by light reflections off the interface of the polished end surface of the mated connectors and air. What is High. Optical return loss for individual events, i. the reflection above the fiber backscatter level, relative to the source pulse, is called reflectance.