Swept And Stepped Measurement Modes - Agilent Technologies 86038A User Manual

Description of the 86038A Measurement Concepts

Swept and Stepped Measurement Modes

The measurements performed by the 86038A involve tuning the laser
source while observing changes in the recovered RF amplitude and phase.
The wavelength can be changed in either a stepped or a swept mode. The
stepped mode offers the best wavelength accuracy resolution and
sensitivity, while the swept mode offers the highest measurement speed.
For more information on measurement modes, refer to "CD/PMD" on
page 97.
Stepped mode
In the stepped mode, the user enters values of start and stop wavelengths
and wavelength increment (step). The system calculates a series of target
wavelengths to which the laser is then tuned. The wavelength resolution
of the resulting measurement is strongly influenced by the choice of
wavelength increment but is also a function of the modulation frequency,
discussed elsewhere.
The stepped mode provides higher wavelength accuracy than the swept
mode, because the dynamics of sweeping the TLS and keeping the
amplitude/phase detection in unison are not required.
The user may elect to use a wavelength meter to optimize wavelength
accuracy. When enabled, this function checks the wavelength accuracy of
the TLS at a series of wavelengths distributed across the user-selected
measurement wavelength range. The observed wavelength errors are
averaged to obtain a single wavelength correction offset value that is used
to correct the wavelength scale of following measurements.
The wavelength correction factor is determined during a normalization (if
the 86122A wavelength meter was detected at startup) and this factor is
automatically applied to future DUT measurements. This arrangement
saves measurement time compared with measuring the wavelength before
each measurement or measuring the wavelength on a point-by-point basis
during the measurement itself. This economy is made possible by the
extremely high wavelength stability, repeatability and linearity of the
tunable laser.
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Agilent 86038A Optical Dispersion Analyzer, Third Edition