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. A significant signal loss in the optical fiber can cause unreliable transmission. How can we know the value of losses on the fiber link? Read on, this post will teach you how to calculate the losses in optical fiber and judge the fiber link performance. It is the power attenuation of the signal after passing through the device. Losses can be introduced by various means such as intrinsic material absorption, scattering, bending, connector loss and more.