An optical power meter head is a modular, interchangeable sensor unit that connects to an optical power meter mainframe or interface. The term usually refers to a device used for measuring the average power in fiber optic systems. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power. An optical power meter (OPM) measures the power levels of light signals in devices that transmit data or power using light. Amplifiers: The electrical signals from the. Figure 1.