Typically both transmitters and receivers have receptacles for fiber optic connectors, so measuring the power of a transmitter is done by attaching a test cable to the source and measuring the power at the other end. An optical power meter (OPM) is a device used to measure the power in an optical signal. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power. The most basic fiber optic measurement is optical power from the end of a fiber. This measurement is the basis for loss measurements as well as the power from a source or presented at a receiver. An OPM uses a photodiode to generate an electrical current proportional to optical power.
