App-2
IM AQ6370D-01EN
Appendix 2 Data Calculation Algorithms for
Spectrum Widths
The AQ6370D can calculate spectrum widths of waveforms being displayed. This section
provides four types of spectrum width calculation methods as well as algorithms for the
NOTCH width calculation.
THRESH Method
This method is used to obtain the spectrum widths of two points, which are lower than
the peak level by a threshold value (THRESH [dB]) specified by a parameter, as well as
their center wavelengths.
The followin table shows the details of parameters for the THRESH method.
Parameter Abbreviation Default Value Setting Range Unit Description
THRESH TH 3.00 0.01 to 50.00 dB Threshold value
THRESH K K 1.00 1.00 to 10.00 - Multiplying factor
MODE FIT MODE FIT OFF ON / OFF - Set whether the half of
maximum point is aligned to
the mode peak or not.
Algorithms differ depending on the number of mode peaks. Algorithms for these numbers
are described below.
In the case of one mode peak
Value
Δλ
λ
1
λ
2
• Perform a mode search to obtain the mode peak.
• Set the wavelengths, which cross the line below the mode peak by the threshold value
(THRESH[dB]), to λ
1
and λ
2
.
• Use the following equations, which incorporate multiplication by the multiplying factor
K for λ
1
and λ
2
, to obtain new λ
1
and λ
2
.
λ'C = (λ
2
+λ
1
)/2
λ
1
= K × (λ
1
− λ'C) + λ'C
λ
2
= K × (λ
2
− λ'C) + λ'C
• Obtain the spectrum width from the following equation.
Δλ = λ
2
−λ
1
• Obtain the center wavelength λC from the following equation.
λC = (λ
2
+λ
1
)/2
Note
If “MODE FIT” is set to ON in the case of a one mode peak, the spectrum width Δλ and the
center wavelength λC will become as follows.
Δλ = 0.0000nm
λC = center wavelength of the mode peak
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