Chapter 1
Principle of Measurement
Principle of optical power and attenuation measurements
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User Manual 770000102/08
Principle of optical power and attenuation measurements
Power
measurements
A power meter, is all that is needed to measure emitted or received
power:
–
to measure emitted power, connect the power meter directly to the
output of the optical emitter;
–
to measure the power at the input of an optical receiver, the power
meter is connected to the end of the fiber, at the point where the
optical receiver would be connected.
Attenuation
measurements
(optical link
loss)
For measurement of the attenuation of power in a complete link or in
elements such as sections of fiber, connections or optical components, a
light source and a power meter are required.
This attenuation is usually deduced from the measurement of optical
power at two points:
Attenuation A
(dB)
= P1
(dBm)
- P2
(dBm)
To perform accurate measurements, the following conditions are neces-
sary
–
Use a light source which is stable both in time and as a function of
temperature.
–
Make sure that all connections and fibers and the receiving cell are
perfectly clean.
–
Use a reference link between the laser source and the test subject.
If several measurements are to be made under identical light injec-
tion conditions, this reference fiber must not be disconnected during
the period while measurements are taking place.
NOTE
To measure the widest range of reflection coefficient, it is necessary
to insert a variable optical attenuator between the reflectometer and
the link to be tested. This attenuator enables the level of the trace to
be adjusted so as to avoid saturation of the reflectometer by the
reflection to be evaluated.
Laser light
source
Reference
fiber
Link under test
Power meter of the
MTS/T-BERD
2000/4000
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MTS2100 4100 Module US rev08.book Page 4 Jeudi, 1. août 2013 1:43 13