Agilent Technologies 86038B User Manual page 109

Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition
Max CD range Based on the chosen wavelength interval and
modulation frequency, the maximum measurable dispersion
(positive or negative) is displayed. This can be compared to the
expected CD when choosing these parameters. Measurement of
a fiber or component with CD higher than this maximum may
have errors due to phase wrapping.
Tips on the Modulation Frequency Selection
• Use the Max CD range display or the selection chart in
Chapter 2 to choose a combination of wavelength increment
and modulation frequency that will avoid phase wrapping
errors and aliasing errors. For example, when measuring
high dispersion fibers, use a small wavelength increment to
avoid aliasing. This increases test time. To reduce test time,
lower the modulation frequency and increase the wavelength
increment.
• Changing the modulation frequency between normalization
and device measurements causes a loss/gain offset due to the
frequency response details of the optical receiver and the
network analyzer RF circuitry. This point is true even when
PDA correction is not selected. If the frequency is changed
after the normalization measurement, the normalization will
become invalid. In this case, DGD/PDL measurements will
not be performed before the normalization is redone. Simple
GD/CD measurements will be performed, to allow quick
assessment of different parameter sets, but the results will
not be normalized.
• The shape of the PDA error changes significantly for different
modulation frequencies, so, if the modulation frequency is
changed, a normalization with PDA should be performed. For
more information on PDA, refer to
Accuracy" on page
• A good rule of thumb is to use a modulation frequency that is
less than 1/20 of the free spectral range of any ripple to be
measured. For example, a 500 MHz modulation frequency
could be used to explore ripple with 10 GHz FSR (or about an
80 pm period at 1550nm) with an attenuation of about 5% of
the ripple peak-to-peak value.
"Phase Dynamic
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