In order 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. Optical loss is measured in “dB” which is a relative measurement, while absolute optical power is measured in “dBm,” which is dB relative to 1mw optical power Loss is a negative number (like –3. 2 dB) while power measurements can be either positive (greater than the reference) or negative (less than. dB loss in fiber optics is the reduction in light signal strength as it travels through a fiber cable, measured in decibels. dB does not indicate how much power exists. 5 dB per kilometer depending on the type and wavelength. Total length of the fiber optic cable.
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