HP 86037B, Instruction Manual

Page: 143 / 204

5-23
Maintenance
Cleaning Connections for Accurate Measurements
The soft core, while allowing precise centering, is also the chief liability of the
connector. The soft material is easily damaged. Care must be taken to mini-
mize 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 connectors are used, the nickel silver can be
pushed onto the glass surface. Scratches, fiber movement, or glass contamina-
tion 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 immedi-
ately obvious to the naked eye, bad measurements can be made without the
user even being aware of a connector problem. Although microscopic exami-
nation and return loss measurements are the best way to ensure good connec-
tions, they are not always practical. An awareness of potential problems, along
with good cleaning practices, can ensure that optimum connector perfor-
mance is maintained. With glass-to-glass interfaces, it is clear that any degra-
dation of a ferrule or the end of the fiber, any stray particles, or finger oil can
have a significant effect on connector performance.
Figure 5-9 shows the end of a clean fiber-optic cable. The dark circle in the
center of the micrograph is the fiber’s 125
µ
m core and cladding which carries
the light. The surrounding area is the soft nickel-silver ferrule. Figure 5-10
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 precision polish lost, but this action can grind off the
glass face and destroy the connector.
Figure 5-11 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 on one connector end can
be transferred to another good connector that comes in contact with it.
The cure for these problems is disciplined connector care as described in the
following list and in
“Cleaning Connectors” on page 5-27 .
Use the following guidelines to achieve the best possible performance when
making measurements on a fiber-optic system:
• Never use metal or sharp objects to clean a connector and never scrape the
connector.
• Avoid matching gel and oils.