Tektronix OM4006D, User Manual, Page: 38 / 205

Getting started
Equivalent-time (ET)
oscilloscopes setup
See the following fi gure for how to connect the OM4000 instrument to
take measurements with real-time oscilloscopes (Tektronix DSA8300 or
DSA8200 sampling oscilloscopes). Appendix E has more information on using
an ET oscilloscope to take measurements. (See page 123,
Equivalent-Time (ET)
oscilloscope operation .)
Figure 2: Equivalent-time (ET) oscilloscope setup diagram
The most important difference between the real-time (RT) and equivalent-time
(ET) oscilloscope measurements is the need for a coherent reference signal for ET
oscilloscopes. The TX reference signal is picked off before the modulator, using a
PM
fi ber cable, with a total path length equal to the path from the splitting point to
the Signal Input on the OM4000 Receiver. Use a SMF fi ber cable to connect the
DUT to the Signal Input connection on the OM4000.
Since the laser phase noise is a real-time quantity, it must be suf fi ciently
suppressed so that it can be tracked in the available bandwidth of the ET scope.
As an example, consider a laser with frequency noise given by
f(t) = f
0
+f
D
sin 2 π f
n
t
If this laser signal is split and then input to the Signal Input and Reference Input
of the OM4000, the resulting beat frequency will be
f
m
(t) ≈ (2 π f
D
f
n
∆ t) sin 2 π f
n
t
14 OM4000D Series Coherent Lightwave Signal Analyzer