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Appendix B Checking Optical Fiber
Cables for Transmission Loss
Measure the optical power to check the spliced joints and aligned joints and to detect
transmission loss errors due to dirty optical connector end faces, etc., following the steps
below.
Have the following ready for this purpose.
• Optical power meter: 2 (one of them with a reference light emitting function)
• Reference single-core cord: 2 (about 1 meter long)
(1) Optical power meter check
Using one of the two optical power meters as a light source, connect them as shown
in figure B-1, and check the light emitting power.
Figure B-1 Measuring Light Emitting Power
Measure the light emitting power using two reference single-core cords.
The reason for using two reference cords is to confirm that the cords are normal.
Normally, the results will be about the same.
(2) Measuring an actual optical transmission line for transmission loss
Connect the power meters to both ends of the optical transmission line and measure
transmission loss.
The difference between the value measured at the light receiving end and the value
measured with the reference cords is the actual transmission loss of the line.
Actual transmission loss of transmission line = Value measured with reference cords
- Value measured of transmission line
The transmission loss thus measured includes the transmission loss of the optical
fiber and the connection loss of splicing and aligner.
(3) Comparing with level diagrams
If a transmission line has an abnormally large transmission loss in comparison with
the level diagrams prepared in the design stage, check the parts constituting the
transmission line, assuming that there must be something wrong with them.
If spliced joints exist, the cable manufacturer will measure the transmission loss of
the transmission lines.
Be sure to measure the transmission loss of your transmission lines.
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Optical power meter (Light emitting end)
Optical power meter (Light receiving end)
Reference single-core cord
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