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Making Measurements
Cleaning Connections for Accurate Measurements
tor pressure. Also, if a piece of grit does happen to get by the cleaning
procedure, the tighter connection is more likely to damage the glass.
Tighten the connectors just until the two fibers touch.
• Keep connectors covered when not in use.
• Use fusion splices on the more permanent critical nodes. Choose the
best connector possible. Replace connecting cables regularly. Frequently
measure the return loss of the connector to check for degradation, and
clean every connector, every time.
All connectors should be treated like the high-quality lens of a good
camera. The weak link in instrument and system reliability is often the
inappropriate use and care of the connector. Because current connec-
tors are so easy to use, there tends to be reduced vigilance in connec-
tor care and cleaning. It takes only one missed cleaning for a piece of
grit to permanently damage the glass and ruin the connector.
Measuring insertion loss and return loss
Consistent measurements with your lightwave equipment are a good
indication that you have good connections. Since return loss and inser-
tion loss are key factors in determining optical connector performance
they can be used to determine connector degradation. A smooth, pol-
ished fiber end should produce a good return-loss measurement. The
quality of the polish establishes the difference between the “PC” (phys-
ical contact) and the “Super PC” connectors. Most connectors today are
physical contact which make glass-to-glass connections, therefore it is
critical that the area around the glass core be clean and free of
scratches. Although the major area of a connector, excluding the glass,
may show scratches and wear, if the glass has maintained its polished
smoothness, the connector can still provide a good low level return
loss connection.
If you test your cables and accessories for insertion loss and return
loss upon receipt, and retain the measured data for comparison, you
will be able to tell in the future if any degradation has occurred. Typ-
ical values are less than 0.5 dB of loss, and sometimes as little as 0.1
dB of loss with high performance connectors. Return loss is a measure
of reflection: the less reflection the better (the larger the return loss,
the smaller the reflection). The best physically contacting connectors
have return losses better than 50 dB, although 30 to 40 dB is more
common.