The logarithmic scale turns link-budget multiplication into addition — that's why dBm is everywhere in photonics.
| dBm | mW | Typical context |
|---|---|---|
| −30 | 0.001 (1 µW) | Detector sensitivity scale |
| −10 | 0.1 | Attenuated receive power |
| −3 | 0.5 | One arm of a 3 dB coupler |
| 0 | 1 | Reference point |
| +3 | 2 | Typical SLD output |
| +10 | 10 | Typical DFB output |
| +13 | 20 | DFB-1550-NLW typical |
| +20 | 100 | High-power DFB |
| +27 | 500 | Pump module typical |
dBm is a logarithmic scale referenced to 1 mW. Its advantage: every gain or loss along the link (in dB) simply adds to the power (in dBm) — launch +10 dBm, subtract 0.5 dB splice, 3 dB splitter and 2 dB of fiber over 10 km, and the receiver sees 10 − 0.5 − 3 − 2 = +4.5 dBm. No multiplication needed.
Mental math: 3 dB ≈ ×2, 10 dB = ×10; combine them for everything else — +17 dBm = 10 × 2 × 2 ≈ 50 mW; −6 dBm = 1/4 mW = 0.25 mW.
Related tools: dB↔linear ratio · PD responsivity
※ Formulas on this page assume ideal models; all device parameters shown are typical values — refer to the datasheet and the serialized factory test report shipped with each unit. For selection support, contact sales@lncetek.com.