Agilent Technologies 8504B, User Manual

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FINAL TRIM SIZE : 7.5 in x 9.0 in
P erforming Guided Setups and Calibrations
P erforming Manual Calibrations
Reduce the eects of
chromatic dispersion at
1550 nm
Y ou can turn o the use of chromatic dispersion correction data. This allows
you to use your own correction methods .
When making measurements at 1550 nm, the amount of chromatic dispersion
experienced by the light traveling in the reference path will be less than that
in the path of the device being tested. This is due to that fact that, in most
cases , light traveling in the path with the device being tested is all in ber .
However , part of the reference path is in an open beam (inside the 8504B).
This mismatch in dispersion results in a broadening and subsequent drop in
the peak value of the displayed reection \impulse".
The peak value decreases monotonically as a function of the length of the
dispersion mismatch. This eect is consistent and has been corrected out by
the precision reectometer . The instrument assumes a dispersion coecient
of 17 ps/(nm)(km). The result of this correction leaves a residual error on the
order of 60.3 dB . If the path to the device being tested is both in ber and an
open beam, the eects are very dicult to remove from the measurement;
subsequent uncertainties due to chromatic dispersion can approach 5 dB .
External sources can be
used
In addition to the internal 1300 nm and 1550 nm sources , you can use an
external source for measurements . (The external source input is provided as
a convenience for users with very advanced applications . It is not meant for
the typical user .) The external source must be able to be modulated with a 27
kHz signal. When using an external source , normal calibration and correction
features are not applied to the measurement data. Refer to \T o calibrate for
an external source " to learn how to calibrate the precision reectometer for
use with an external source .
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