Measuring Loss; Basic Theory - OPTOKON OFT-920 User Manual

9

Measuring loss

9.1 Basic theory

Loss measures the signal degradation in a fiber optic cable. The light source injects
an optical signal of the appropriate wavelength into the fiber and the power meter
measures the received signal at the same wavelength.
There are two different measuring methods:
• Method 6
• Method 7
according to IEC 874-1 4.4.7.4.
Power measurement is the basis of optical testing and determines the power budget
of the fiber optic link by comparing the power of the transmitter and the sensitivity of
the receiver. This difference is the maximum acceptable loss. The power loss is
caused by different phenomena such as attenuation of the fiber, dirty connector
mating faces, connector misalignment, loss of splices and other events as sharp
bends of fiber...
The "end to end" loss test is the most often used acceptance test of power loss in
fiber optic links. The test is based on measuring the power difference at the input
and output of the link.
One or two OFT-920 instruments are used for this test, where the light source port
acts as a transmitter and the optical power meter port as a receiver.
The "end to end" test has two steps:
1. Setting the reference
2. Measuring the loss
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OFT-920 USER MANUAL