Keysight Technologies 86120B, User Manual

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52
Using the Multi-Wavelength Meter
Defining Laser-Line Peaks
Defining Laser-Line Peaks
The Agilent 86120B 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 excursion 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 unmodulated 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 signals. For example, a laser that is
amplitude modulated in the audio frequency range can cause spurious wavelengths
to be displayed below and above the correct wavelength. The power of these spuri-
ous wavelengths is below that of the correct wavelength. These spurious signals can
be eliminated by decreasing Peak threshold from its Preset value.
Peak excursion The peak excursion defines the rise and fall in amplitude that must take place in
order for a laser line to be recognized. The rise and fall can be out of the noise, or in
the case of two closely spaced signals, out of the filter skirts of the adjacent signal.
The peak excursion’s default value is 15 dB. Any laser line that rises by 15 dB and
then falls by 15 dB passes the rule. You can set the peak excursion value from 1 to
30 dB.
8 dBm – 2 dBm 10 dB – =
( )