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MTS
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OTS Measurement principles
•
the backscattering coefficient of the fiber used.
In order to measure the largest range of reflection coefficient, a variable optical
attenuator must be inserted between the OTDR and the link under test. This
attenuator allows the level of the curve to be adjusted so that the OTDR is never
saturated by the reflection to be measured.
OTS Measurement principles
Attenuation measurement
The attenuation measurement in power of a complete link or elements such as
fiber sections, connections, optical components, requires a calibrated laser light
source and a power meter.
This is generally deducted from the optical power measurement at two points:
Loss A
(dB)
= P1
(dBm)
- P2
(dBm)
Important
To make accurate measurements the following conditions are
required:
•
Use a light source that is stable in time and in respect to the temperature.
•
Verify that the connections, the fibers and the receiving cell are perfectly
clean.
•
Use a reference link between the laser source and the element under test. To
make several measurements with the same light injection conditions, the
reference fiber must not be disconnected during the measurement period.
Two methods are used to measure the fiber optic attenuation:
•
The cut fiber method
•
Insertion loss measurement method
Cut fiber method
1.
The power P1 at the output of the fiber under test is measured, then the fiber
is cut approximately two meters from the extremity at the source end.
Typical values of backscattering coefficient for a 1ns pulse
for a singlemode fiber
- 79 dB at 1310 nm
- 81 dB at 1550 nm and 1625 nm
for a multimode fiber
- 70 dB at 850 nm
- 75 dB at 1300 nm
Calibrated
laser light
source
Reference
fiber
Link under test
Powermeter
1
2
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