Saving/data-view key - Data-saving, OPM can save up to 1000 data files. backlight control: turn on or turn off the. REF/dB key: Short press the dB to switch unit, click once nW/dBm/dB to enter the upper clear data, press and hold until REF is displayed on the screen, and set the current optical power as reference value, enter the relative optical power test mode, the screen will display the setted reference. Please note that there is no direct method of extracting power from the input signal defined in the matlab code. For a sanity. ments to the instrument's performance and functionality. The figures given in this manual ion of this manual to ensure the accuracy of its contents. However, should you have any questions or fi gistered users with a variety of information and services. In this article, learn: What is an optical power meter? An optical power meter (OPM) measures the power levels of light signals in devices that transmit data or power using. An optical power meter measures the photon energy in the form of current or voltage from an optical detector such as a semiconductor, a thermopile, or a pyroelectric detector.