Fiber Optic Power Converter

Optical power in fiber optics is measured in dBm or milliwatts (mW).

dBm is a logarithmic unit referenced to 1 milliwatt.

Conversion formulas:

• mW = 10^(dBm / 10)
• dBm = 10 × log₁₀(mW)

Key reference points:

Useful rules of thumb:

• +3 dBm = double the power
• −3 dBm = half the power
• +10 dBm = 10× the power
• −10 dBm = 1/10 the power

Typical fiber optic transmitter power: −5 to +5 dBm. Typical receiver sensitivity: −20 to −30 dBm.

The reason optical power is quoted in dBm rather than milliwatts is that fiber work is all about adding up losses, and logarithms turn multiplication into addition. Every connector, splice, and kilometer of fiber subtracts a predictable number of decibels, so a technician can do the whole “link budget” with simple arithmetic: start at the transmitter’s dBm, subtract the losses along the way, and the result has to land above the receiver’s sensitivity for the link to work.

This is where the 3 dB rule earns its keep. Because 3 dB is exactly half the power, a single dirty or loose connector that adds 3 dB of loss has quietly halved your signal, and two of them quarter it. That’s why a link that tested fine can fail after someone reseats a patch cord badly. Don’t be thrown by the negative numbers either: receivers work happily down at −20 to −30 dBm, a tiny fraction of a milliwatt, because the system is built around detecting very small amounts of light cleanly rather than blasting power down the glass.