6-16
Reference
Cleaning Connections for Accurate Measurements
• Use fusion splices on the more permanent critical nodes. Choose the best con-
nector possible. Replace connecting cables regularly. Frequently measure the
return loss of the connector to check for degradation, and clean
every
connec-
tor,
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 connectors are so easy to use,
there tends to be reduced vigilance in connector 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 indica-
tion that you have good connections. Since return loss and insertion loss are
key factors in determining optical performance they can be used to determine
connector degradation. A smooth, polished fiber end should produce a good
return loss measurement. The quality of the polish establishes the difference
between the “PC” (physical 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, in the future you will be
able to tell if any degradation has occurred. Typical values are less than 0.5 dB
of loss, and sometimes as little as 0.1 dB of loss with high performance con-
nectors. Return loss is a measure of reflection: the less reflections the better.
The larger the return loss, the smaller the reflection. The most physically con-
tacting connectors have return losses better than 50 dB, although 30 to 40 dB
is more common.
book.book Page 16 Monday, January 31, 2000 10:34 AM
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