It turns out that the optical module we wanted to connect isn't establishing a link – it’s not working. What could have gone 'wrong'? And more importantly – how do we check it? Problems with optical modules can generally be divided into three categories:

  • Connection issues
  • Physical damage to the module
  • Incompatibility

No technology is completely fault-proof, which is why it's essential to know how to diagnose optical modules and troubleshoot connection problems.

 

How to Identify Optical Module Incompatibility Issues?

Suspecting an incompatibility issue between the optical module and the network device? Watch for error messages like "unsupported transceiver" or "unknown transceiver," or check if the module works fine on a different device. Always test the module in another port or device to rule out port-specific problems. If the issue persists, start by consulting the technical documentation of the network device to confirm if the module type is supported. Verify that the port's speed and protocol are compatible with the optical module. If everything matches, check the device's firmware and update it to the latest version if necessary.

If the module doesn't work and there are no clear signs of incompatibility, the problem could lie in connection settings or physical aspects. For example, the port might be set to 1 Gbps, while the module is SFP+ 10 Gbps, or there might be damage to the fiber optic cable. Inspecting fiber quality can be done in several ways, such as using an optical microscope for checking cleanliness and an Optical Time-Domain Reflectometer (OTDR) to assess signal quality.

Optical Module Diagnostics with DDM Functionality

What if the problem "follows the module"? To verify module damage, use the Digital Diagnostics Monitoring (DDM) function built into optical modules. DDM is the most effective tool for diagnosing optical modules. It is available in most modern optical modules, including those from LightOptics. It allows real-time monitoring of key parameters, such as:

  • Optical Output and Input Power: Helps determine if the laser is transmitting at the correct power and if the module is receiving a quality signal.
  • Module Temperature: Indicates if the module operates within the proper temperature range.
  • Supply Voltage: Shows whether the module receives the appropriate power.
  • Laser Bias Current: Indicates the state of the laser. A high current can suggest an overloaded or damaged laser.

You can invoke the DDM function, for example, with the command # show transceiver detail in CLI.

Analyzing DDM Parameters

  1. Module Temperature
    1. Excessive temperature can impact module performance and signal quality, potentially leading to permanent damage.
  2. Supply Voltage
    1. Low or unstable voltage may result in erratic module operation and laser issues.
  3. Laser Bias Current
    1. A bias current higher than usual may indicate a damaged laser consuming too much power. In extreme cases, the device might automatically shut down the laser to prevent further damage.
    2. A lack of bias current indicates a completely non-functional laser.
  4. Laser Optical Power
    1. Low output power (Tx power) may indicate a damaged transmitter laser, possibly “burned out.” This can be confirmed by comparing the displayed value with the module's technical documentation.
    2. Low input power (Rx power) suggests a receiver issue or problems along the connection, such as a dirty fiber optic cable.

Compare all readings to the values in the optical module's technical documentation to identify deviations from the norm. Additionally, check that DDM readings remain stable during transmission. Sudden fluctuations, like spikes in laser current, can indicate unstable and faulty operation.

Readings Indicate Incorrect Values – What to Do?

If the issue lies in low input power readings (Rx Power), dirt contamination might be the culprit. Clean the module and fiber optic ends. Just as a dirty window limits the amount of light entering a room, a contaminated optical module or fiber will hinder the laser signal from reaching the photodiode. In severe cases, this could be perceived as a lack of signal by the switch. If cleaning doesn’t help, inspect the connection route for potential damage.

In other cases, if the readings indicate the previously mentioned errors, replacing the optical module might be necessary.

Summary

Every device has its unique characteristics and challenges; there is no perfect product. Regularly monitoring the condition of both the optical modules in the system and the fiber optic connection is essential. The DDM function in optical modules allows real-time control over parameters such as output power, laser current, and temperature, helping to quickly identify physical damages like a burned-out laser.

All modules and AOC and DAC cables in the Fibermarkt store come with a 2-year warranty. We offer technical support before and after purchase. Contact us via phone, email, or chat on our website.