Agilent Technologies 86122A User Manual page 44

Setting Up the 86122A Cleaning Connections for Accurate Measurements
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 insertion
loss are key factors in determining optical connector 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, 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 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.
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 imperfections not touching the fiber core may not affect
performance (unless the imperfections keep the fibers from contacting).
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Agilent 86122A Multi-Wavelength Meter, Second Edition