Agilent Technologies 86121A, User Manual, Page: 46 / 240

Defining Laser-Line Peaks 3
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Defining Laser-Line Peaks
The Agilent 86121 WDM Channel Analyzer uses two
rules to identify valid laser-line peaks. Understanding
these rules is essential to getting the most from your
measurements. For example, these rules allow you to
“hide” AM modulation sidebands or locate laser lines
with small amplitudes.
In order to identify a laser line, the laser-line must meet
both of the following rules:
• Power must be greater than the power established by
the peak threshold limit
• Power must rise and then fall by at least the peak excur-
sion value
In addition, the input wavelength range can be limited
as described in this section.
Peak threshold
limit The peak threshold limit is set by subtracting the peak
threshold value from the power of the largest laser line.
So, if the largest laser line is 2 dBm and the peak
threshold value is 10 dB, the peak threshold limit is
–8 dBm . You can set the
peak threshold value between 0 to 40 dB.
The peak threshold’s default value is 10 dB. This
ensures that any modulated signals being measured are
not confused with their AM sidebands. For unmodu-
lated lasers, or Fabry-Perot lasers, it may be desirable
to increase this threshold to look for responses that are
more than 10 dB from the peak.
Peak threshold can be used to suppress spurious sig-
nals. For example, a laser that is amplitude modulated
in the audio frequency range can cause spurious wave-
lengths to be displayed below and above the correct
wavelength. The power of these spurious wavelengths
is below that of the correct wavelength. These spurious
signals can be eliminated by decreasing Peak threshold
from its Preset value.
8 dBm – 2 dBm 10 dB – =
( )