A good dBm (decibel-milliwatt) level for fiber optic communication typically ranges from -3 dBm to -9 dBm. This range ensures optimal signal strength and quality for data transmission over fiber optic cables. 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. Every fiber link loses some light along the way, and that loss is expressed in dB because the decibel scale makes it easy to add up small losses across long distances. The lower the dB loss, the higher the quality of the signal, and the farther it can travel without significant degradation.