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Choosing Setup Parameters
Background
Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition
This section presents the mathematical relationships on which
the group delay and dispersion measurements are based. You
will see how wavelength resolution and measurement sensitivity
depend on the instrument setup parameters. This knowledge
will help you to effectively resolve group delay ripple, avoid
phase wrapping errors, avoid aliasing errors, and improve the
repeatability (reduce the noise) of chromatic dispersion and
relative group delay measurements.
The Agilent 86038B employs the modulation phase shift
method. Light is intensity modulated with an RF tone and
applied to the device under test. The transmitted (or reflected)
signal is detected to recover the modulation envelope, and the
envelope phase is measured relative to the RF source. Any
change in the group delay ∆τ of the test device produces a
corresponding change in the modulation phase. In practice, the
wavelength is stepped or swept and the change in the group
delay ∆τ for each wavelength increment is calculated from the
measured change in phase according to:
Equation 1
where ∆φ is the phase change in degrees produced by a small
wavelength step, fm is the modulation frequency in Hz, and the
subscript ∆λ indicates that the change in group delay being
measured was produced in response to an incremental change
in wavelength. The first term on the right side of
the fraction of cycles of modulation phase shift produced by the
wavelength change. The second term is the time period of a
single RF cycle (1/freq = period). The product of the two terms
has units of time.
1
-----
Δλ
360
f
m
Equation 1
is
61
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