Relationship Of Setup Parameters To Imaging - Agilent Technologies 86038B User Manual

Since the modulation frequency limits the wavelength
resolution, if a wavelength increment is chosen significantly
smaller than this resolution in swept-wavelength
measurements, the 86038B performs a Gaussian smoothing on
the data at the relevant resolution. This reduces noise while
maintaining the true resolution.
Figure 12 Adjusting wavelength step and mod. freq. to achieve desired
resolution

Relationship of setup parameters to imaging

Since the 86038B uses AM modulation, it is actually sampling at
the two AM sidebands simultaneously with the carrier
wavelength, and reporting the average result. This causes the
dependence of resolution on frequency. Again there is an
implication for detecting features between the sampled points.
Even if the wavelength increment is arbitrarily small, the RF
modulation sideband separation must be small compared to the
wavelength spacing over which the device under test has
variations of interest. If the RF modulation sideband separation
is more than the wavelength increment, these two different
sample points can cause imaging.
Consider an example of a narrow band-pass filter being
measured with a very small wavelength increment and an RF
modulation frequency so large that each sideband is stepped
through the filter pass band while the other sideband is well
rejected. For this example the pass band would appear at two
wavelengths, each incorrect in wavelength by half the sideband
separation, and each attenuated in amplitude.
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Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition