To use a power meter for fiber optic testing, always clean connectors first with lint-free wipes or click-to-clean tools. Select the correct wavelength and set your reference. You measure optical power in dBm or insertion loss in dB. Consistent procedures ensure accuracy. tested and known to be fine) that is attached to the transmitter, acting as the 'source' to measure transmitter power. So, Exactly an optical power meter is a small device that tells you how strong the optical signal, it likes a thermometer but instead of checking your temperature, it checks the strength of optical laser going through the fiber cable.