Agilent Technologies Agilent 86120C manual Inspecting Connectors

Making Measurements

Cleaning Connections for Accurate Measurements

The soft core, while allowing precise centering, is also the chief liabil- ity of the connector. The soft material is easily damaged. Care must be taken to minimize excessive scratching and wear. While minor wear is not a problem if the glass face is not affected, scratches or grit can cause the glass fiber to move out of alignment. Also, if unkeyed con- nectors are used, the nickel silver can be pushed onto the glass sur- face. Scratches, fiber movement, or glass contamination will cause loss of signal and increased reflections, resulting in poor return loss.

Inspecting Connectors

Because fiber- optic connectors are susceptible to damage that is not immediately obvious to the naked eye, poor measurements result with- out the user being aware. Microscopic examination and return loss measurements are the best way to ensure good measurements. Good cleaning practices can help ensure that optimum connector perfor- mance is maintained. With glass- to- glass interfaces, any degradation of a ferrule or the end of the fiber, any stray particles, or finger oil can have a significant effect on connector performance. Where many repeat connections are required, use of a connector saver or patch cable is recommended.

Figure 2- 6 shows the end of a clean fiber- optic cable. The dark circle in the center of the micrograph is the fiber’s 125 ∝m core and cladding which carries the light. The surrounding area is the soft nickel- silver ferrule. Figure 2- 7 shows a dirty fiber end from neglect or perhaps improper cleaning. Material is smeared and ground into the end of the fiber causing light scattering and poor reflection. Not only is the preci- sion polish lost, but this action can grind off the glass face and destroy the connector.

Figure 2- 8 shows physical damage to the glass fiber end caused by either repeated connections made without removing loose particles or using improper cleaning tools. When severe, the damage of one con- nector end can be transferred to another good connector endface that comes in contact with the damaged one. Periodic checks of fiber ends, and replacing connecting cables after many connections is a wise prac- tice.

The cure for these problems is disciplined connector care as described in the following list and in “Cleaning Connectors” on page 2- 47.

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