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IM AQ1200-01EN
Optical Pulse Measurement and
Analysis Conditions
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App
Index
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Explanation
Index of Refraction
The Instrument uses indices of refraction in the calculations that it performs to measure distance. If
you do not set the correct index of refraction, the distance measurement will be incorrect.
The Instrument has the following preset indices of refraction that correspond to each wavelength.
1310 nm: 1.46000
1550 nm: 1.46000
1625 nm: 1.46000
1650 nm: 1.46000
You can specify a value from 1.30000 to 1.79999.
Backscattering Light Level
Light that travels through an optical fiber displays a phenomenon known as Rayleigh scattering. Due
to this phenomenon, a portion of the light is sent backwards, in the direction opposite to the direction
of propagation. This phenomenon is known as backscattering. The backscattering light level setting is
used when the Instrument calculates the return loss and total return loss. If you do not set the correct
backscattering light level, the return loss and total return loss measurements will be incorrect.
The Instrument has the following preset backscattering light levels that correspond to each wavelength.
1310 nm: –50 dB
1550 nm: –52 dB
1625 nm: –53 dB
1650 nm: –53 dB
You can specify a value from -10.00 to -64.99.
Approximation Method
When the Instrument calculates splice loss, it extrapolates straight lines. These straight lines are
known as approximated lines.
There are the following two kinds of approximated lines.
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Least squares approximation (written as LSA below)
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Two point approximation (written as TPA below)
LSA
The Instrument calculates the loss between two points by using the least squares method on all the
data between the two points.
This method has the following characteristics.
Merits: Because all the data between the two points is used, errors in the calculated value
are small.
Fluctuations in the calculated values are reduced, and highly reproducible values can
be obtained.
Demerit: If a large reflection or splice loss is present in the section whose loss is being
calculated, those values are also included in the calculation, so large errors result.
If no reflection and splice loss events are present in the section being calculated, the LSA provides
a value that has a smaller degree of error than the TPA.
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Approximated line
calculation range
3.6 Setting Analysis Conditions
