Operating basics
The linear average is obtained using a two-step process:
The impulse response associated with the signal is calculated by a
deconvolution process
That impulse response is applied to the known data content of the signal to
produce a linear average.
The linear average assumes that the signal has a linear dependence on the data
bits. If there is nonlinearity, for example if the crossing point is higher than 50%,
then the linear average is a poor
fi
t to the actual waveform.
The linear average can provide useful information about the nature of the signal.
The length of the impulse response is set by Averaging: Number of Symbols in
Impulse Response. Typically the average eye diagram appears noisier as the
impulse response length is increased, because the number of traces in the eye
diagram increases. However if the true impulse response of the signal has a long
duration, for example if there is a re
fl
ection from a length of RF cable inside the
transmitter, then the linear average eye diagram will clean up once the impulse
response length is made long enough to capture that re
fl
ection event.
There are several options of which tributaries to take into account when calculating
the impulse response, selected from Averaging: Tributaries contributing to
average. The basic option is Same trib only, which typically gives the cleanest
result. It is possible to include other tributaries and exclude the same tributary, for
example Other SOP tribs. This setting computes the impulse response only by
taking into account the signal on the other state of polarization. For an ideal signal
the linear average computed this way should be a
fl
at line. If there is structure on
the linear average waveform then that suggests there is a crosstalk mechanism
between the states of polarization.
The impulse response variables are available in the MATLAB workspace in
variable Imp, which has
fi
elds .XRe, .XIm, .YRe and .YIm.
OM4000D Series Coherent Lightwave Signal Analyzer
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Summary of Contents for OM4006D
Page 2: ......
Page 6: ......
Page 22: ...Compliance information xvi OM4000D Series Coherent Lightwave Signal Analyzer...
Page 24: ...Preface xviii OM4000D Series Coherent Lightwave Signal Analyzer...
Page 100: ...Taking measurements 76 OM4000D Series Coherent Lightwave Signal Analyzer...
Page 146: ...Appendix D Automatic receiver deskew 122 OM4000D Series Coherent Lightwave Signal Analyzer...
Page 202: ...Appendix H Cleaning and maintenance 178 OM4000D Series Coherent Lightwave Signal Analyzer...
Page 205: ...Index W Waveform averaging 48 OM4000D Series Coherent Lightwave Signal Analyzer 181...