EXFO FTB-5500B PMD Analyzer - Manual (Page 111)

Polarization Mode Dispersion Analyzer 103
B Using Third-Party Broadband
Light Sources
You can use broadband light sources from a third-party supplier in
combination with the FTB-5500B Polarization Mode Dispersion Analyzer.
However, the broadband source must respect a few simple, basic criteria
in order not to impair the normal operation of the analyzer or degrade
some of its specifications.
Compliance Criteria
³
Criterion 1: Source Modulation
Ideally, the light emitted from the broadband source and launched into
the device under test must be free of any periodic power-modulation
or phase-modulation. Nevertheless, a periodic modulation will not
impair the normal operation of the analyzer whenever the following
condition is respected:
Equation 1
where f
m
is the fundamental frequency of the periodic modulation. In
other words: the fundamental frequency of the periodic modulation
must be higher than 500 kHz. Even more generally speaking, the
smallest frequency in the spectrum of the modulation waveform must
be higher than 500 kHz.
³
Criterion 2: Source Spectrum
The adequacy of the broadband source spectrum can be judged easily
through a precise quantitative criterion. The basic characteristic of the
broadband source spectrum that is relevant is the rms width of its
corresponding auto-correlation. The auto-correlation corresponds to
the Fourier transform of the spectrum. It is a function of delay τ. You
can have a good estimate of the auto-correlation by saving the
displayed interferogram when the broadband source is connected
directly to the interferometer input with a patchcord.
f
m
500 kHz ≥