Reference Test Jumper
Cables and Mating Adapters
conditioning is generally required for multimode and
singlemode launch cables attached to a source. Multimode
cables generally use a mandrel wrap mode conditioner (see
here and here)
and a LED source but special modal conditioning patchcords
are available. Singlemode fiber just needs a 30mm loop to
ensure the launch cable is singlemode.
- In order to test cables in an
insertion loss test or with an OTDR, one needs to
establish test conditions. For insertion loss
testing, this requires reference launch jumper
cables to connect the test source to the cable under
test and receive cables to connect the fiber optic
power meter. For accurate measurements, the launch
and receive cables must be made with fiber and
connectors matching the cables to be tested and
terminated carefully to ensure low loss.
- Insertion loss testing
two or three reference cables, depending on
the test performed and the appropriate mating
adapters for the connectors. Reference cables for
insertion loss testing with a light source and power
meter are typically 1-2 meters long, with fiber and
connectors matching the cables to be tested.
- OTDR reference/launch cables
are also used to isolate the large reflectance from
the instrument connector as well and need to be much
longer, typically ~100 meters for multimode and ~1
km for singlemode.
- The accuracy of the
measurement will depend on the quality of the
reference cables, since they will be mated to the
cable under test and the connection loss is measured
against the connector on the reference cable. To
provide reliable measurements, launch and receive
cables must be in good condition and kept very
clean. They can easily be tested against each other
to insure their performance. Connector mating
adapters are used to connect the cables under test
to the launch and receive cables. Only the highest
performance bulkhead splices should be used, and
their condition checked regularly, since they are
vitally important in obtaining low loss connections.
The quality and cleanliness of
the connectors on the launch and receive cables is
one of the most important factors in the accuracy of
loss measurements. Always test reference cables by
the patchcord or single ended method (FOTP-171,
reversing the cables to test connectors on both
ends) to make sure they are in good condition before
you start testing other cables.
- Standards groups have not been
able to successfully specify the quality of
reference cables in terms of tightly toleranced
components like the fiber and connectors. Standards
which call for special reference quality test cables
now specify cables with low loss connections. The
best recommendation for qualifying reference cables
is to choose cables with low loss, tested
"single-ended" per cable test standard FOTP-171.
Connector-to-connector mating adapters are used to
connect reference cables to the cables being tested.
Only the highest quality mating adapters should be
used for testing, as they are a factor in loss also.
Inexpensive adapters generally have plastic mating
sleeves to align the connector ferrules which wear
out quickly, causing high loss with even good
connectors. Use only mating adapters with metal or
preferably ceramic mating sleeves which are
specified for both multimode and singlemode
Use - Creating a "Launch Cable"
find yourself in the field without a set of
reference cables, you can always test patchcords or
other cables, even fibers in a cable you are
testing, against other cables and use any low loss
cables as reference cables.
For a insertion loss testing with a meter and
source, you can use one fiber as a launch cable
and loopback fibers from the far end of the
cable to test other fibers. You will need to take
the meter to the far end of the cable and calibrate
the output of the launch cable. It's easier to
do this with two sets of meters and sources, but can
be done with one.
fibers back at the end of the cable. Remember each
loopback added includes the attenuation from two fiber
lengths and two connector losses!
you are testing a multi-fiber cable that's
long enough to test with an OTDR and you have
already tested it with an OLTS (like standards
require) so you know the fiber is good, you
can use one of the fibers in the cable as a
launch cable. Set up as below and simply have
another tech connect up the fiber being used
as the launch cable to the other fibers to
test each of them. If you want to test from
one end by yourself, loopback from the far end
and then use the two fibers as the launch
cable to connect up to other fibers from the
same end as the OTDR (second drawing.) If you
have access to both ends, you can continue
looping back and get many fibers on one trace,
to the length capability of the OTDR.
Installed Cable Plants
of fiber optic measurements