To measure optical loss, you can use two units, namely, dBm and dB. While dBm is the actual power level represented in milliwatts, dB (decibel) is the difference between the powers. If the optical input power is P1 (dBm) and the optical output power is P2 (dBm), the power loss is. Fiber Optic Measurement Units: "dB" and "dBm" Whenever tests are performed on fiber optic networks, the results are displayed on a power meter, OLTS or OTDR readout in units of “dB. A decibel is expressed as the base 10 logarithm of the ratio of the power of two signals, as shown here: 10 is the base 10 logarithm, and P1 and P2 are the powers to be compared. 10 is different from the Neparian. dB loss in fiber optics is the reduction in light signal strength as it travels through a fiber cable, measured in decibels.
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