Measurement and Calibration of Optical Power Meter

Optical power meter calibration ensures accurate measurement of optical power by comparing the device under test to traceable reference standards under controlled conditions.

Overview of Calibration

Calibration of an optical power meter involves establishing a precise relationship between the readings of the meter and known optical power values. This is achieved by comparing the device under test (DUT) to a working standard, which is itself calibrated against a reference standard traceable to a national metrology institute such as NIST (USA), PTB (Germany), or NPL (UK) under defined reference conditions . This traceability ensures that measurements are internationally recognized and reliable.

Calibration Methods

Optical power meters are typically calibrated using either collimated beams or connectorized fiber configurations. The calibration process accounts for the spectral responsivity of the detector, which may be made of silicon (Si), germanium (Ge), or indium gallium arsenide (InGaAs), and is highly dependent on the wavelength of the incident light . Common calibration wavelengths for telecommunications applications are 850 nm, 1300 nm, and 1550 nm, though other wavelengths such as 670, 780, and 980 nm may also be used .

Calibration Procedure

1. Preparation: Ensure the optical detector is clean and free from contamination. Check for any performance issues before calibration .
2. Reference Standard Measurement: Use a highly accurate thermal detector or calorimeter as a transfer standard. This standard is calibrated against a national standard to provide traceable power values .
3. Comparison: Measure the optical power from a laser source using both the DUT and the transfer standard. Adjust the DUT readings to match the reference values.
4. Wavelength and Connector Matching: Calibrate the power meter using the same fiber type and connector configuration that will be used in practice, as reflected power from connectors can introduce measurement errors .
5. Documentation: Record calibration results, including uncertainties, linearity, and any corrections applied. Certificates of calibration are issued according to ISO 9001 or ISO/IEC 17025 standards .

Special Considerations

• Detector Characteristics: Temperature stabilization and spectral responsivity data are important for high-accuracy measurements .
• Uncertainty: Ensure that the measurement uncertainty of the power meter is within acceptable limits for your application .
• Linearity Testing: Optional linearity tests can verify that the meter responds proportionally across its measurement range .
• Special Calibration Services: Manufacturers like Keysight offer metrology-grade calibration options to achieve the lowest measurement uncertainties for critical applications .

Conclusion

Proper calibration of optical power meters is essential for accurate and reliable optical measurements. By following traceable procedures, using appropriate reference standards, and considering detector and connector characteristics, users can ensure their optical power meters provide precise readings suitable for telecommunications, research, and industrial applications .