Hello, everyone!
Today I will continue to write about FTTA testing. Now, I will explain IL testing FTTA cables.
OLTS or OPM, test source and referent cables are used for IL measurements. IL testing is done at wavelengths that will be used in the system. Also, attention should be paid to the direction of measurement. All testing should be like a real system. Test source can have different sources (LED, VCSEL, FB laser) with different wavelengths, 850 and 1310 nm are most often used for MM fibers, while 1310 and 1550 nm are most often used for SM fibers. The test source is always used with the reference cable. The OPM is an optical power meter that displays the optical power in mW or dBm, which only needs to be selected with the buttons on the instrument. Can be used with or without a reference cable. The reference cable is a tested cable with 0 dB attenuation, the length of this cable is usually about 1 to 2 m.
There are three testing methods, depending on the cable to be tested. There are the following methods:
single-ended (only TS has a reference cable, it is used for testing short cables, e.g. patch cords),
double-ended (TS and OPM use reference cables, it is used for long optical cables) and
method with three reference cables (it is used for specific cables, with specific connectors, e.g. ribbon cable with MPO/MTP connectors).
The double-ended method is used for IL testing FTTA cables. It means that both TS and OPM have reference cables. There are two variants of IL testing. First, one technician is on the ground, the other is at the top of the tower. Both have OPM and TS and do IL testing as I described. Another way, one technician is on the ground and has both TS and OPM, another technician is on top of the tower and switches the optical fibers using a fiber loop – loopback(as shown in the picture above). The fiber loop should be about 20 m. Both methods of measuring IL can be used. This second method is more common because it is safer.
This is the end of this article. In the next article, I will explain OTDR testing >> Testing FTTA (3): OTDR testing.
Thank you!
