HP 83487A, User Manual, Page: 88 / 98

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Reference
Cleaning Connections for Accurate Measurements
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.
Visual inspection of fiber ends
Visual inspection of fiber ends can be helpful. Contamination or imperfections
on the cable end face can be detected as well as cracks or chips in the fiber
itself. Use a microscope (100X to 200X magnification) to inspect the entire
end face for contamination, raised metal, or dents in the metal as well as any
other imperfections. Inspect the fiber for cracks and chips. Visible imperfec-
tions not touching the fiber core may not affect performance (unless the
imperfections keep the fibers from contacting).