Tektronix OM4006D, User Manual

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Core Processing function reference
CentFreq – real value, optical frequency of signal compared to multiple of
1/Delay BalancedDiffDetection – 0 = single-ended detection; 1 = balanced
detection
BoundValsIn – structure of boundary values from previous block
AlertsIn – structure of alerts accumulated before executing function v –
structure giving optical power at output of delay discriminator:
.t0 – time of fi rst symbol
.dt – symbol duration
.Values – 1xN or 2xN array of values (real or complex)
BoundValsOut – structure of boundary values to be passed to next block
AlertsOut – structure of alerts including any alerts raised during execution of
function
DiffDetection simulates the insertion of an optical passive delay discriminator
into the path of the signal. This mode of optical detection does not use coherent
detection, but is a form of self-homodyne detection. It is described in [1] for
BPSK modulated signals and [2] for QPSK.
Output parameter v records the optical power at the output of the delay
discriminator. For BPSK modulation formats (SigType = 1,3) the delay
discriminator has the form of [1], while for QPSK it is as described in [2]. For
QPSK formats the result is given as complex numbers, where each value refers to
power in one arm + i * power in other (quadrature) arm
The optical power in one output arm (single-ended detection) is reported
if BalancedDiffDetection = 0, or the difference in powers between two
balanced outputs when BalancedDiffDetection = 1. Input parameter p may be
a single-polarization or dual-polarization representation. Output v is always
a single-polarization variable. The delay within the delay discriminator is of
duration Delay. The standard delay discriminator con
fi guration uses one symbol
of delay.
CentFreq sets the offset between the center of the signal spectrum and a comb
of frequencies at multiples of 1/Delay. For a real implementation of a delay
discriminator to work well the signal optical frequency should be a multiple
of 1/Delay. This is achieved either by tuning the signal laser or adjusting the
delay over a small range. The variable CentFreq allows a non-optimal delay
discriminator con
fi guration to be simulated. Use CentFreq = 0 to obtain the
standard operating condition.
References K. Yonenaga, S. Aisawa, N. Takachio, K. Iwashita, "Reduction of four-wave
mixing induced penalty in unequally spaced WDM transmission system by using
optical DPSK," IEE Electron. Lett., vol. 32, no. 23, p. 1218-1219, 1996.
96 OM4000D Series Coherent Lightwave Signal Analyzer