Agilent Technologies 86038B User Manual page 128

128
fit, ax
3rd Order Sellmeier
dispersion-unshifted fiber, in which material dispersion is
dominant.
5th Order Sellmeier The 5th-order Sellmeier fit,
4 2 -2
ax +bx +c+dx +ex
instabilities in the measurement path, provides more general
purpose curve fitting. The five-term Sellmeier fit can yield
multiple zero-dispersion wavelengths. All the values and
their associated slopes are shown in the graphs. The system
searches for dispersion zeros in a wavelength range equaling
approximately five times the measurement span (2.5 times
each side of the center wavelength). This allows
identification of zero-dispersion wavelengths which fall
outside of the measurement range. In some cases, due to the
peculiarity of the five-term Sellmeier fit, zero-dispersion
wavelengths found outside of the measurement range may
not correspond to actual zero-dispersion wavelengths of the
device under test. This fit often provides the lowest RMS
Error of the various fits, so it's deviation is useful for
assessing noise and short-period ripple.
Equation Area
Displays the general form of the selected equation and
additional information like parameter values specific to the
selected curve fit.
Deviation Only
The trace displays the difference between the measured data
and the curve fit. This is useful to evaluate a fit and for
evaluating trace ripple.
Hide Original Trace
Removes the original trace from the graph so that only the curve
fit trace is visible.
Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition
2 -2
+b+cx , is commonly used for
-4
, although more affected by noise and