Absolute power measurement is not as expected.

Applies to

All fiber optic power meters


When measuring absolute power, the result is significantly different than expected.

Troubleshooting steps

‚ÄčPossible Cause 1: The incorrect measurement units are selected.

Proposed Solution: 

  • To measure absolute power values, the units need to be set to either dBm, or Watt/milliwatt.
  • Please double-check that you have selected the correct units.


Possible Cause 2: The light source used is modulated or incompatible.

Proposed Solution:

  • Most EXFO power meters are designed to be used with a continuous wave (CW) light source, that is not modulated.
  • Turn off the source modulation if possible or use a different light source.
  • Refer to this knowledge article for information on EXFO light source and power meter compatibility.


Possible Cause 3: The input power is higher than the power range of your power meter.

Proposed Solution:

  • Attenuate the signal so that it falls into the range of your power meter model ( check specification sheet).
  • Use a power meter suitable for high power measurements.
  • EXFO used an X or a -H to identify high-power meters. For example FPM-302X or PX1-H.