dbm on dbmW is a unit of level used to indicate that a power level is expressed in decibels with reference to one milliwatt. Optical power has a vast range of practical values, easily ranging from the output power of an EDFA in watts (W), all the way down to the Rayleigh backscatter level of single-mode fiber in femtoWatts (fW). This represents a difference of 15 orders of magnitude! If you are measuring an EDFA or any other optical power between 1W and 10pW, please check out or new optical powermeter the OPM-200. On the other hand, if you need to measure the fiber backscatter, check our new OFDR system, the SPA-100. In order to work with such a wide range of values, optical power is often represented on logarithmic scale as dBm. dBm is a logarithmic scale that expressed optical power relative to 1 milliwatt (1 mW) as a reference point.