How to measure optical power in optical cables

Use an optical power meter with a matching light source to measure the strength of light in a fiber optic cable, ensuring connectors are clean and the correct wavelength is selected.

Tools Needed

• Optical Power Meter (OPM): Measures light strength in dBm or mW. Most meters use photodiode sensors (Si, Ge, or InGaAs) suitable for fiber optic wavelengths .
• Light Source: Laser or LED that emits light at the wavelength used in your fiber network.
• Reference Patchcords: For calibration and accurate measurement.
• Cleaning Tools: Lint-free wipes or click-to-clean tools to clean connectors .

Step-by-Step Procedure

1. Prepare the Equipment: Turn on the optical power meter and allow it to warm up for 1–2 minutes for stable readings .
2. Clean Connectors: Always clean both the fiber ends and the meter adapters to prevent dust or dirt from affecting measurements .
3. Set Wavelength: Match the power meter's wavelength to the light source wavelength (commonly 850 nm, 1310 nm, or 1550 nm) to ensure accurate readings .
4. Connect the Fiber: Attach the fiber to the light source and then to the power meter. For end-to-end testing, use a reference patchcord if measuring source power or disconnect the cable from the receiver if measuring at the far end .
5. Read the Measurement: The meter will display optical power in dBm. Record the value and compare it to expected levels or insertion loss limits for your network .

Additional Tips

• Insertion Loss Measurement: Combine a light source and power meter to measure total signal loss, including connectors and splices. This is often called the “one-jumper method” .
• OTDR Testing: For long cables with splices, an Optical Time Domain Reflectometer can verify individual splice quality and locate faults .
• Calibration: Regularly calibrate your power meter to maintain accuracy and comply with industry standards .
• Safety: Never look directly into the fiber end when the light source is active, as laser light can damage eyes .

By following these steps, you can accurately test the optical power of a fiber optic cable, verify network performance, and ensure that the cable meets the required specifications.