Optical-Power Measurement

The power level in optical communications is of too wide a range to express on a linear scale. A logarithmic scale known as decibel (dB) is used to express power in optical communications.

The wide range of power values makes decibel a convenient unit to express the power levels that are associated with an optical system. The gain of an amplifier or attenuation in fiber is expressed in decibels. The decibel does not give a magnitude of power, but it is a ratio of the output power to the input power.

Loss or gain = 10log10(POUTPUT/PINPUT)The decibel milliwatt (dBm) is the power level related to 1 milliwatt (mW). Transmitter power and receiver dynamic ranges are measured in dBm. A 1-mW signal has a level of 0 dBm.

Signals weaker than 1 mW have negative dBm values, whereas signals stronger than 1 mW have positive dBm values.

September 4, 2011

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