Keysight N778xC Series Polarization Instruments User’s Guide 49
Definition of Terms 3
Polarization Mode Dispersion (PMD)
The arithmetic average of the differential group delay (DGD) over a broad
specified wavelength span (here unless otherwise noted 100 nm).
Polarization Mode Dispersion (PMD) Error
The PMD error is given by the deviation of the measured PMD and the
PMD of the golden device.
Conditions: Measurement settings and operation mode as specified.
Wavelength span and wavelength increment as specified.
Polarization Mode Dispersion (PMD) Repeatability
The agreement of repeated measurements of PMD on a stable test device
and under constant environmental conditions, expressed as:
PMDi denotes the measured PMD and StDev denotes the standard
deviation over repetitions i.
Polarization Mode Dispersion (PMD) Vector
The PMD vector represents the polarization dependence of the group
delay (GD). For a given wavelength, the magnitude of the PMD vector is
the Differential group delay (DGD) at that wavelength, and the vector
direction corresponds to the fast principal state of polarization in Mueller
notation. The PMD vector is denoted by:
In highly mode-coupled devices, such as standard single mode fibers of
kilometer length, the DGD depends on wavelength. Stress or
temperature change may change the dependence of DGD on wavelength
significantly. It can be shown that the DGD characteristics of such
devices can be described statistically by PMD.
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