Agilent Technologies 11898A, User Manual

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3-13
Reference
Cleaning Connections for Accurate Measurements
• Keep connectors covered when not in use.
• 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 connector performance they can be used to
determine connector degradation. A smooth, polished fiber end should pro-
duce a good return-loss measurement. The quality of the polish establishes
the difference between the “PC” (physical contact) and the “Super PC” con-
nectors. 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 con-
nection.
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. 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 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.