Viavi MTS 4000 Base Unit, Руководство пользователя

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Chapter 5 Power meter, VFL (Visual Fault Locator) and Talkset
Principle of optical power and attenuation measurements
66 User Manual 77000000206 Rev. 007
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 vital
– 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.
Insertion loss method
1 The power meter is first connected to the laser source via the refer-
ence fiber: P1 is measured.
2 Then the fiber to be tested is inserted between the reference fiber
and the power meter: P2 is measured.
The difference between P2 and P1 gives the attenuation of the fiber
under test.
Laser light
source
Reference
fiber
Link under test
Power meter of the
4000 Platform
1
2