When combined with a light source, the instrument is called an Optical Loss Test Set, or OLTS, and is typically used to measure optical power and end-to-end optical loss.OverviewAn optical power meter (OPM) is a device used to measure the power in an signal. The term usually refers to a device. 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. Optical Power Meter and accuracy is a contentious issue. The accuracy of most primary reference standards (e.g.,, Length,, etc.) is known to a high accuracy, typically of the orde.