48 Keysight N778xC Series Polarization Instruments User’s Guide
3 Definition of Terms
DOP Uncertainty
The DOP uncertainty is defined to be twice the standard deviation of the
DOP from the ideal value:
DOP
i
denotes the measured DOP value and StDev denotes the standard
deviation over repetitions i.
If DOP is given in %, the DOP uncertainty has the same unit.
Measurement: The polarization state of a signal with nominally 100%
polarized light is randomly scrambled. The readout deviations from 100%
are recorded over all polarization states and wavelengths.
Differential Group Delay (DGD)
The dependence of the group delay at a fixed wavelength resulting from
applying all possible polarization states, expressed as the difference
between the maximum and the minimum group delay value.
Differential Group Delay (DGD) Error
Specifies the error of the measurement results for differential group delay,
expressed as the sum of an offset and a standard deviation.
The offset is calculated by the difference of the mean value of the golden
device data and the mean value of the measured data, both mean values
calculated over the wavelength.
The standard deviation over wavelength is calculated from the deviations
around a calibration line shifted by this offset, again over wavelength.
• Conditions: Stable device-under-test.
• Measurement: Using a standard SM fiber with nominally 0 ps DGD and
various PM fibers with specified DGD over the specified wavelength
range.
Differential Group Delay (DGD) Measurement Range
Specifies the range of DUT DGD values for which the instrument measures
DGD values not disturbed by aliasing effects.
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