Fiber Optic Decibel Conversion

Decibels are used to express optical loss in fiber optic link, by representing the difference in optical power at the output and input sides of the link.

The chart below helps to clarify a common misunderstanding regarding what the term "decibel" actually represents. A decibel is a power ratio, rather than an absolute number. Decibels are a measurement of optical power as expressed on a logarithmic scale that begins at 1 milliwatt.

Because decibels represent a logarithmic rather than linear progression, note that 10 dB is not twice the power of 20 dB.

Since a decibel is not an absolute number, this measurement provides a way to ensure that a specific fiber optic link will not exceed design specifications for attenuation, regardless of the wavelength used.

Finally, decibels, which are whole numbers, are easier to express than milliwatts, which are typically fractions. This advantage can be seen in the chart, Converting Power to MilliWatts.