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Taking measurements
Figure 6: Multicarrier setup window
Multicarrier channel List. The main part of this section is the channel de fi nition
table. There are two types of channel de fi nition table: absolute and relative.
The default table type is absolute. A relative table may be entered by selecting
Channel List Options: Add channel list: Add a new relative channel list. With an
absolute channel de
fi nition table the channel frequencies speci fi ed are the actual
optical frequencies, in the region of 195 THz. If the table is relative then the
frequencies refer to the difference between the channel frequency and the current
local oscillator frequency. Relative frequencies are speci
fi ed in gigahertz.
The absolute channel de fi nition table has four columns:
The Channel column contains an integer identifying the channel. The values
in this column do not have to be consecutive. The Frequency column contains
the absolute channel frequency.
The Preferred LO is the frequency that the local oscillator (also called the
Reference Laser) is tuned to during an automatic scan to observe that channel.
If the bandwidth of the multicarrier channels are so large that only one
channel can be observed at a time given the bandwidth of the oscilloscope,
then the Preferred LO is typically set to the same value as Frequency. If the
channels have smaller bandwidth, then several table rows may be set to the
same Preferred LO (even though the Frequency is different) so that all those
channels are captured at the same local oscillator setting. This can save time,
because tuning the local oscillator may be slow.
OM4000D Series Coherent Lightwave Signal Analyzer 67