Tektronix OM4006D, User Manual

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Core processing software guide
5. OUI retrieves output variables from MATLAB workspace
6. OUI displays output variables as eye diagrams, constellation diagrams,
numerical values, etc.
In fact when the record size is larger than the block size multiples calls to
CoreProcessing are executed for each oscilloscope record. This mode of
processing is known as block processing. (See page 87,
Block processing .)
To customize the signal processing of the OM4000, the user must modify
the commands in the OUI’s MATLAB Commands Window, or modify
CoreProcessing.m, or both. Commands can be added to the MATLAB Commands
Window following the call to CoreProcessing if additional processing is desired
after CoreProcessing has completed. If deeper changes to the signal processing
are needed then it is necessary to modify CoreProcessing.m.
This Section will discuss the code in CoreProcessing.m, and how it derives the
output variables from the scope record Vblock.
MATLAB variables
MATLAB is a loosely typed language. All numerical variables are created as reals
by default, and arrays and structured variables are sized as they are created and
manipulated. The core processing software follows some rules of its own with
regard to variable structure and naming. A variable representing a quantity that
varies with time is a structured variable having (at least) three
fi elds:
.t0 – time of fi rst element in seconds
.dt – time separation between elements
.Values – actual values of elements
The time dimension of the .Values fi eld extends from left to right, dimension 2 in
MATLAB terms. The number of rows of the .Values fi eld depends on the nature
of the variable it represents. A voltage has one row of real numbers. A phase
factor has one row of complex numbers. The electric
fi eld of an optical signal
has two rows of complex numbers, for the two states of polarization, and can be
thought of as a row of Jones vectors. Similarly, a Stokes vector as a function of
time has three rows of reals.
Variables representing a Jones vector vs. time typically begin with “p”. Variables
representing a phasor factor, having inphase and quadrature components, begin
with “z”. Variables having sample times at the center of the symbols in a digital
comms signal contain the letters “Sym”. Variables representing the X or Y
polarizations contain the letter “X” or “Y”. Variables representing the inphase
part of a signal contain “Re”, and the quadrature part contain “Im”.
For example, the X polarization of a signal at the symbol centers is stored in
variable zXSym. The data sequence (e.g. PRBS sequence) encoded on the inphase
part of the X polarization of a signal is de
fi ned in variable PattXRe.
80 OM4000D Series Coherent Lightwave Signal Analyzer