iXBlue ModBox VNA, Руководство пользователя

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ModBox VNA – User’s Manual
Ref. Ed. B – 12/05/2020 32
Appendices
A
M
ACH
-Z
EHNDER INTENSITY MODULATORS
Lithium niobate (LiN
b
O
3
) Mach-Zehnder Modulators (MZM) are external
modulator that have been widely used since the mid-nineties, mostly in long
haul optical networks for their ability to modulate optical signal from 1300 and
1550 nm laser diodes with short transition times and without chirp compared to
direly modulated diode lasers. Thanks to their broad wavelength performance,
they currently also offer modulation solutions in the NIR band, and for even
shorter wavelengths.
MZM are 2-waves interferometer devices that exhibit a sine transfer function
(Fig.13). Although MZMs are highly stable components, their operating point
suffers from slow drifts due to variations of external conditions (mechanical
strengths, te mperature, radiation …). Those drifts may induce key performances
time fluctuations (extinction ratio for example).
In order to adjust MZM operating point independently from the applied RF
modulating signal, we could use a RF design based on 2 sets of electrodes: the
RF set (the RF electrodes) is used to apply the RF signal (PRBS data stream,
analog signal, short pulses). The DC electrodes are used to set the modulator’s
operating set point. Fig.14 illustrates the typical electrode architecture of LiN
b
O
3
MZM.
Figure 17: MZM transfer function and data output vs data input at QUAD+ and QUAD- operating point