P (dBm)=10log 10 (P (mW)/1 mW) In optical communications, typical values are strongly negative. For instance, an LED source may output around –20 dBm, while laser or VCSEL -based test sources may operate near –10 dBm. 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 loss is P1 - P2. 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. ” Optical loss is measured in “dB” which is a relative measurement, while absolute optical power is measured in “dBm,”. An SFP (Small Form-factor Pluggable) is a hot-pluggable, standardized transceiver module that converts electrical signals from a switch or router port into optical or copper signals for fiber or copper links. 9 dB, its overload point is -4. Receive power is the power at which the receiver of an optical transceiver module receives optical signals, in dBm.