Absolute Power measurement appears outside of specifications (small error)

Applies to

All fiber optic power meters


When measuring Absolute Power in dBm or milliwatt, you observe a small measurement error. This could be observed in a laboratory or manufacturing environment.

Troubleshooting steps


Possible Cause 1: Incorrect FOA type is being used.

Proposed Solution:

  • FOA = Fiber Optic Adapter and is the part screwed on to the power meter detector receptacle.


  • FOA-3XX series should be used in lab power meters, and FOA-XX should be used on field power meters.
  • PX1 has a different type of adapter called FOAS.



Possible Cause 2: The light source type may be inappropriate.

Proposed Solution:

  • EXFO power meters are calibrated with narrow band laser sources.
  • When using other source types ( LED, Fabry Perot, other) small variations are normal.


Possible Cause 3:The wavelength is not selected correctly.

Proposed Solution:

  • Sometimes light sources have nominal wavelength, but the true wavelength is different.
  • For accurate measurements, it is best to measure the wavelength of the source, and set the power meter as close as possible to the same wavelength.


Possible Cause 4: There is dirt or contamination in the optical path.

Proposed Solution:

  • Inspecting and cleaning the FOA, the fiber end-face, and the detector window will help eliminate this possible source of error.


Possible Cause 5: The warm up period is not completed.

Proposed Solution:

  • To achieve full performance, some lab power meters require a warm-up and/or temperature stabilization period.


Possible Cause 6: A Calibration or Repair may be required.

Proposed Solution:

  • If on inspection, you observe that the detector window is scratched or otherwise damaged, a repair is required. On most power meters this part can be replaced. Please request an RMA for repair.
  • Your power meter may require a calibration. Please request an RMA for calibration.