A class of "high power" meters has some type of optical attenuating element in front of the detector, typically allowing about a 20 dB increase in maximum power reading.OverviewAn optical power meter (OPM) is a device used to measure the power in an signal. The term usually refers to a device for testing average power in systems. Other general purpose light power measuring. The major types are (Si), (Ge) and (InGaAs). Additionally, these may be used with attenuating elements for high optical power testing, or wavelengt. A typical OPM is linear from about 0 dBm (1 milli Watt) to about -50 dBm (10 nano Watt), although the display range may be larger. Above 0 dBm is considered "high power", and specially adapted units may measure u.