Always use an optical power meter or OTDR to measure your signal. If your signal is too strong, use optical attenuators. Optical Signal Attenuation is the single greatest factor limiting the distance and performance of your network. This guide will demystify signal loss, explore its causes, and show you how. The measurement may be optical power from a test source, a transmitter or the input of receiver, measured in dBm, which is "absolute" power - absolute in that it refers to power calibrated to a national standard, so two people testing the same fiber output with different power meters calibrated to. Perhaps the most important test is insertion loss of an installed fiber optic cable plant performed with a light source and power meter (LSPM) or optical loss test set (OLTS) which is required by all international standards to ensure the cable plant is within the loss budget before acceptance of. Optical power loss (attenuation) refers to the reduction of signal strength as light propagates through fiber. Understanding and managing it is critical to. Signal loss within a system is expressed using the decibel (dB), which is a measure of signal power attenuation. The relationship is: 1mw=0dbm, that is to say, 2mw=3dbm, 10*lgmw is the dbm value.