Calibration and Wavelength of Optical Power Meter

Optical power meters must be calibrated at specific wavelengths to ensure accurate measurements, typically using NIST-traceable standards at 850, 1300, and 1550 nm.

Calibration Overview

Calibration of an optical power meter establishes the relationship between the meter's readings and known reference power values under controlled conditions. This is done by comparing the device under test (DUT) to a working standard, which is itself calibrated against a national standard such as NIST in the U.S., PTB in Germany, or NPL in the UK, ensuring international traceability and equivalence of measurements . Calibration typically involves measuring the meter's response at multiple power levels and wavelengths, then generating a calibration table stored in the meter.

Wavelength Considerations

Optical power meters are highly wavelength-dependent because their photodiode sensors—commonly silicon (Si), germanium (Ge), or indium gallium arsenide (InGaAs)—respond differently to different wavelengths . The telecommunications industry primarily uses 850 nm, 1300 nm, and 1550 nm, but other applications may require 670, 780, or 980 nm. Diode lasers used in calibration emit light within ±10 nm of the nominal wavelength, and temperature variations can shift the emission, affecting meter readings . Therefore, the meter should ideally be calibrated using the same fiber type and connector configuration as in actual use to minimize errors caused by reflections or spatial profile differences .

Calibration Procedure

1. Power On and Zeroing: Turn on the meter and zero it with no light incident on the sensor .
2. Wavelength Selection: Set the meter to the wavelength corresponding to the system under test .
3. Reference Comparison: Measure the output from a calibrated laser source or transfer standard and compare it to the meter reading .
4. Adjustment and Documentation: If deviations exceed specifications, the meter's internal calibration table is adjusted, and a certificate is issued with the verified wavelengths and power levels .
5. Periodic Calibration: Annual calibration is recommended, as meters can drift 0.05–0.2 dB per year due to detector aging, temperature cycling, and connector wear .

Practical Notes

• Always clean fiber connectors before measurement to avoid contamination errors .
• Use the same fiber and connector type during calibration and actual measurements to reduce reflection-induced errors .
• Track calibration due dates and cross-check against a known reference meter between calibrations . By following these procedures and considering wavelength-specific responses, optical power meters can provide accurate, reliable measurements essential for fiber optic system testing and maintenance.