Agilent Technologies 86038A User Manual page 38

Measurement Concepts
38
• When measuring DGD, any GD drift or disturbance of the DUT GD during the
scan time of each measurement can bias the measurement point to higher DGD.
This effect might be seen as a single measurement point spike if the DUT or fib-
ers were bumped during the measurement. Note that DGD is far more sensitive
to this than PDL.
• When making precision DGD measurements, use the Real Time Port Monitor to
verify GD drift before normalizing or measuring. Fiber connectors are a frequent
cause of GD drift and must be clean to a much higher standard than commonly
needed for fiber optic measurements of insertion loss. Fibers require protection
from normal room air currents. Fibers need to be secured and allowed time to
settle after handling. Refer to "Real-Time Port Monitor" on page
• When making PDL or DGD measurements, the polarization scanner runs at a
fixed speed and produces PDL or DGD changes with the majority of spectral
content around 8 Hz. This limits the minimum IF bandwidth when scanning to
70 Hz, which avoids attenuating the 8 Hz components. Using a wider IF band-
width allows a faster measurement, but raises the noise in the measurement
and may slightly bias DGD and PDL toward larger values.
• During PDA normalization, 70 Hz IF bandwidth is used to characterize noise
components with the scanner off, for both GD and Magnitude. These noise
measurements provide the best correction of DGD and PDL when measuring in
a 70 Hz IF bandwidth. Refer to "Phase Dynamic Accuracy" on page
• PDL and DGD may indicate negative values, which are clearly not possible. This
results from noise in the measurement. Negative values are useful when
smoothing across wavelength sample points to obtain an unbiased estimate of
the average DGD or average PDL.
Understanding the Attributes Being Measured
Agilent 86038A Optical Dispersion Analyzer, Third Edition
94.
108.