App-4
IM AQ6376-01EN
ENVELOPE Method
This method is used in conjunction with a straight line (envelope) connecting mode
peaks to obtain the spectrum widths of the two points, which are lower than the peaks by
a configured threshold value (THRESH [dB]), as well as their center wavelengths. The
following table shows the details of parameters for the ENVELOPE method.
Parameter Abbreviation Default Value Setting Range Unit Description
THRESH 1 TH1
3.00
0.01 to 50.00
dB
Threshold value
THRESH 2 TH2
13.00
0.01 to 50.00
dB
Lower limit value when
the number of modes is
calculated
K K
1.00 1.00 to 10.00
-
Multiplying factor
Algorithms differ depending on the number of valid mode peaks. Valid mode peaks mean
the mode peaks, among the mode peaks obtained from a mode search, whose level
(LOG) is equal to or greater than the line that is below the peak level by the lower limit
(THRESH2). Algorithms for these numbers of valid modes are described below.
In the case of one valid mode peak.
Threshold
Value
Δλ
λ
1
λ
2
λ
C
• 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
1
- 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.
λ
C = (
λ
2
+
λ
1
)/2
Appendix 2 Data Calculation Algorithms for Spectrum Widths
