Check the module s optical power

You can check an optical module's transmit (Tx) and receive (Rx) power using CLI commands, Digital Optical Monitoring (DOM/DDM), or an optical power meter.

Using CLI Commands on Network Devices

For Cisco switches, you can monitor SFP optical power via CLI:

1. Verify the module is recognized: Run show inventory to confirm the SFP is detected, including part number and serial number .
2. Check interface status: Use show interface status to ensure the port is up and connected .
3. Read optical power and diagnostics: Execute show interfaces transceiver detail or show interface transceiver detail to view:
   • Tx Power (dBm): Light emitted by the module
   • Rx Power (dBm): Light received from the remote device
   • Temperature, voltage, and laser bias current For Huawei devices, the command display interface transceiver verbose provides similar information, showing Current TX Power and Current RX Power in dBm .

Using Digital Optical Monitoring (DOM/DDM)

Many modern SFP modules support DOM/DDM, which allows real-time monitoring of optical power directly from the switch or router. DOM readings include:

• Transmit and receive power
• Module temperature
• Voltage and bias current Compare the measured Tx/Rx values with the module's datasheet to ensure they are within the recommended range. Deviations beyond ±3 dB can cause bit error rate (BER) issues or link instability .

Using an Optical Power Meter

For precise measurements, especially in lab or troubleshooting scenarios:

1. Connect the fiber to an optical power meter (OPM).
2. Measure the transmitted power from the module.
3. Compare readings to the module specifications to detect degradation or excessive loss .

Interpreting Results

• Low Rx Power: Often indicates fiber attenuation, dirty connectors, or a failing remote module .
• Low Tx Power: May suggest a failing laser in the module .
• High or low alarms: Many modules provide warning flags for optical power, temperature, or voltage thresholds . Regular monitoring of optical power helps prevent intermittent link issues, packet loss, and unnecessary hardware replacement. Always follow safety precautions: do not look directly into fiber ends and clean connectors before testing .