In simple terms, an OPM acts like a “light meter for fiber optics”, allowing engineers to determine how strong or weak an optical signal is at any point in the network. Optical modules are designed to operate within specific optical power ranges. An optical power meter, often shortened to OPM, is the instrument used for that job. For SFP testing, the OPM is especially valuable because it helps verify the actual signal leaving a. Optical Performance Monitoring (OPM) refers to the measurement of optical layer performance parameters — such as wavelength, OSNR, optical power, channel spectrum, and other signal-quality metrics — to assess the health of optical channels.