The Secret of Maintaining Your Fiber Optic Network
By Colin Yao
Why do you need a fiber identifier and what can it do for you?
If you have ever seen a telephone company technician working on the phone jump box outside
your house, you should have noticed a special handheld phone like instrument. The technician
uses it to identify the incoming telephone wires by tapping onto the wires and listening for
a tone. Once he finds the correct wire, he connects the wire into your house.
During fiber optic network installation, maintenance, or restoration, it is also often
necessary to identify a specific fiber without disrupting live service. This battery powered
instrument looks like a long handheld bar and is called fiber identifier or live fiber identifier.
How does it work?
There is a slot on the top of a fiber optic identifier. The fiber under test is inserted
into the slot, then the fiber identifier performs a macro-bend on the fiber. The macro-bend
makes some light leak out from the fiber and the optical sensor detects it. The detector can
detect both the presence of light and the direction of light.
A fiber optic identifier can detect "no signal", "tone" or "traffic" and it also indicates
the traffic direction.
The optical signal loss induced by this technique is so small, usually at 1dB level,
that it doesn't cause any trouble on the live traffic.
What kind of fiber cables does it support?
Fiber optic identifiers can detect 250um bare fibers, 900um tight buffered fibers, 2.0mm
fiber cables, 3.0mm fiber cables, bare fiber ribbons and jacketed fiber ribbons.
Most fiber identifiers need to change a head adapter in order to support all these kinds
of fibers and cables. While some other models are cleverly designed and they don't need to
change the head adapter at all. Some models only support single mode fibers and others can
support both single mode and multimode fibers.
What is relative power measurement
Most high end fiber optic identifiers are equipped with a LCD display which can display
the optical power detected. However, this power measurement cannot be used as a accurate absolute
power measurement of the optical signal due to inconsistencies in fiber optic cables and the
impact of user technique on the measurements.
But this power measurement can be used to compare power levels on different fiber links
which have same type of fiber optic cable. This relative power measurement has a lot of applications
as described below.
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