The signal strength is typically measured in decibels (dBm) and indicates the power level of the signal being transmitted through the fiber optic cable. A good dBm for fiber optic networks is typically around -10 dBm to -20 dBm for optimal performance. If you've found yourself wondering how these terms differ, or when to use one over the other, you're not alone. While they may sound similar, they serve very different purposes in fiber. In optical communications, dB (decibel) is a logarithmic unit used to quantify signal strength, power gain, or loss.