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2-43
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 µm 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.