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Details on the measured signal :
This is a 40Gb/s NRZ modulation realized on a LiNbO3 MZI modulator driven by a 40Gb/s pulse pattern generator sending a 16bits pattern. The blue trace represents the intensity modulation (pulse) and the red trace represents the alpha chirp factor of the modulator.
Measurement setup :
AP2440A benefits :
Time resolved chirp (TRC)
is a key parameter for high speed transmission optimization and an
accurate measurement of this parameter becomes very important for 10Gb/s
and higher speeds.
MZI modulator manufacturers have to inform their customers about chirp characteristics
of the modulator. Instead of using chirp characteristics in GHz, which depends
on pulse characteristics, alpha chirp factor have to be used to qualify properties
of the modulator for every kind of pulse.
The AP2440A is measuring pulse & chirp
characteristics at the same time and therefore can calculate the alpha
chirp factor. This is the most accurate, fast and repeatable instrument
for alpha chirp factor measurement thanks to its optical complex spectral
analysis patented method.
The "Alfa analysis" function of the AP2440A can calculate the average
Alfa value for a defined percentage of the pulse power.
The cause of residual chirp
in MZI-based devices is an unbalanced phase change in the two arms
of the MZI. Chirp arises when the drive voltage is transitioning between
Vnull and Vpeak. So, for MZI modulators only transient chirp is present.
Alpha chirp factor is a small-signal quantity which describes the relationship
between the phase modulation (chirping) and intensity modulation of an optical
signal. So, Alpha chirp factor can be use to qualify properties of a MZI for
every kind of pulse. It is an intrinsic properties of the modulators.