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An optical power meter (OPM) is a testing instrument used to accurately measure the power of fiber optic equipment or the power of an optical signal passed through the fiber cable. It also helps in determining the power loss incurred to the optical signal while passing through the optical media. An optical power meter is made up of a calibrated sensor that measures amplifier circuit and a display. The sensor normally consists of a silicon (Si), germanium (Ge) or indium gallium arsenide (InGaAs) based semiconductor. The display unit shows the measured optical power and the corresponding wavelength of the optical signal.
OPM calibrates the wavelength and measures the power of an optical signal. Before testing, the required wavelength is set manually or automatically. Accurate calibration of the signal wavelength is necessary for accurate measurement of power level, otherwise the test may yield false reading.
Different sensor types used in OPMs have different characteristics. For example, Si sensors tend to become saturated at low power levels and can only be used in 850 nanometer bands, while Ge sensors saturate at high power levels, but perform poorly at low power.
To calculate the power loss, OPM is first connected directly to an optical transmission device through a fiber pigtail, and the signal power is measured. Then the measurements are taken through OPM at the remote end of the fiber cable. The difference between the two measurements displays the total optical loss the signal incurred while propagating through the cable. Adding up all the losses calculated at different sections yields the overall loss incurred to the signal.