EXFO FastReporter 2 - Manual (Page 370)

Measuring Chromatic Dispersion: Theory
360 FastReporter 2
Helping You Manage Chromatic Dispersion
As the previous table demonstrates, specific fits are recommended for
specific types of fiber and specific wavelength ranges. Fits should be used
carefully when extrapolating parameters to obtain maximum precision.

The 3-Term Sellmeier applies mostly to standard fibers with single zero
dispersion at 1300 nm.

The 5-Term Sellmeier has five zero crossings. Since it is extremely
elastic, it should be used with caution when extrapolating because the
fit may curve away from the true results beyond fitted points.

The same warning applies to the cubic fit.

The lambda-log-lambda fit is applicable to dispersion-shifted fibers
with a zero dispersion wavelength in the 1550 nm wavelength region.

The linear fit is useful when there are too few measurements for
multiple parameter fits to be used. It is applicable to all fibers if the
range is sufficiently small.
The fits will give you a tool to obtain the dispersion slope and zero-
dispersion point.
Helping You Manage Chromatic Dispersion
The zero-dispersion wavelength (where dispersion is at zero) corresponds
to the wavelength point at which the fiber under test reaches its maximum
bandwidth.The slope from this zero-dispersion point indicates how fast
dispersion rises as wavelength increases. Key chromatic dispersion
parameters are the dispersion zero and the slope at zero dispersion.
Getting precise chromatic dispersion parameters helps you choose the
right dispersion-compensated fiber or material in order to reverse the
dispersion and dispersion slope before the data is interpreted by the
receiver at the other end of the line.
The effects of chromatic dispersion decrease with a reduction in the
absolute value of the fiber chromatic dispersion or with dispersion
compensation.