Agilent Technologies Agilent 86120C manual Defining Laser- Line Peaks

Making Measurements

Defining Laser-Line Peaks

Defining Laser- Line Peaks

The Agilent 86120C 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 mod- ulation 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 The peak threshold limit is set by subtracting the peak threshold value

limitfrom 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 (–8 dBm = 2 dBm – 10 dB ) . 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 cor- rect wavelength. The power of these spurious wavelengths is below that of the correct wavelength. These spurious signals can be elimi- nated by decreasing Peak threshold from its Preset value.

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