Fiber Dispersion Compensating Module (Dcm) - Agilent Technologies 86038B User Manual

Fiber Dispersion Compensating Module (DCM)

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Since the number of points does not need to be too high, the
time taken by using a lower IF bandwidth like the 70Hz in the
specifications should be acceptable. But a higher rate can be
used if the noise is still acceptable, especially when the fiber
attenuation is not too high.
Alternately, or when a high CD necessitates it, a higher density
of points can be used, together with a higher IF bandwidth to
maintain measurement speed, and the GD results can be
smoothed to the desired resolution to reduce the noise,
especially for the CD calculation.
Since the absolute GD of long fibers can change substantially
with small temperature changes, the measurement time for long
fibers (tens of km) should not be set too high, and the Drift
Correction functionality should be used to reduce drift
sensitivity.
Since the CD uncertainty increases for small values of
wavelength resolution (high resolution), and high resolution is
usually not needed for fiber, the resolution should be kept down
by either using wide wavelength increment or smoothing the
data to a wide resolution. It is recommended to smooth the GD
spectrum and then determine the CD from this, but smoothing
the CD curve itself or a combination of the two gives similar
results.
Fitting the data results in even lower noise, effectively basing
each CD value on all of the points in the fit wavelength range,
with the accuracy dependent on the validity of the chosen fit
type.
Characteristics
• High dispersion (steep change in group delay versus
wavelength).
• Wide wavelength range of interest
• Significant loss
• The zero dispersion wavelength falls far outside the 1500 nm
window.
Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition