Fibre optic splicing
- an overview or tutorial covering fibre optic splicing (fiber optic
splicing) - the way in which it is done and why it is used instead of fibre
optic connectors.
Rather than using optical fibre connectors, it is possible to
splice two optical fibres together. An fibre optic splice is defined by the fact
that it gives a permanent or relatively permanent connection between two fibre
optic cables. That said, some manufacturers do offer fibre optic splices that
can be disconnected, but nevertheless they are not intended for repeated
connection and disconnection.
There are many occasions when fibre optic splices are needed.
One of the most common occurs when a fibre optic cable that is available is not
sufficiently long for the required run. In this case it is possible to splice
together two cables to make a permanent connection. As fibre optic cables are
generally only manufactured in lengths up to about 5 km, when lengths of 10 km
are required, for example, then it is necessary to splice two lengths together.
Fibre optic splices can be undertaken in two ways:
- Mechanical splices
- Fusion splices
The mechanical splices are normally used when splices need to
be made quickly and easily. To undertaken a mechanical fibre optic splice it is
necessary to strip back the outer protective layer on the fibre optic cable,
clean it and then perform a precision cleave or cut. When cleaving (cutting) the
fibre optic cable it is necessary to obtain a very clean cut, and one in which
the cut on the fibre is exactly at right angles to the axis of the fibre.
Once cut the ends of the fibres to be spliced are placed into
a precision made sleeve. They are accurately aligned to maximise the level of
light transmission and then they are clamped in place. A clear, index matching
gel may sometimes be used to enhance the light transmission across the joint.
Mechanical fibre optic splices can take as little as five
minutes to make, although the level of light loss is around ten percent. However
this level of better than that which can be obtained using a connector.
Fusion splices form the other type of fibre optic splice that
can be made. This type of connection is made by fusing or melting the two ends
together. This type of splice uses an electric arc to weld two fibre optic
cables together and it requires specialised equipment to perform the splice. The
protective coating from the fibres to be spliced is removed from the ends of the
fibres. The ends of the fibre optic cable are then cut, or to give the correct
term they are cleaved with a precision cleaver to ensure that the cuts are
exactly perpendicular. The next stage involves placing the two optical fibres
into a holder in the fibre optic splicer. First the ends if the cable are
inspected using a magnifying viewer. Then the ends of the fibre are
automatically aligned within the fibre optic splicer. Then the area to be
spliced is cleaned of any dust often by a process using small electrical sparks.
Once complete the fibre optic splicer then uses a much larger spark to enable
the temperature of the glass in the optical fibre to be raised above its melting
point and thereby allowing the two ends to fuse together. The location spark and
the energy it contains are very closely controlled so that the molten core and
cladding do not mix to ensure that any light loss in the fbre optic splice is
minimised.
Once the fibre optic splice has been made, an estimate of the
loss is made by the fibre optic splicer. This is achieved by directing light
through the cladding on one side and measuring the light leaking from the
cladding on the other side of the splice.
The equipment that performs these splices provides computer
controlled alignment of the optical fibres and it is able to achieve very low
levels of loss, possibly a quarter of the levels of mechanical splices. However
this comes at a process as fusion welders for fibre optic splices are very
expensive.
Mechanical and fusion splices
The two types of fibre optic splices are used in different
applications. The mechanical ones are used for applications where splices need
to be made very quickly and where the expensive equipment for fusion splices may
not be available. Some of the sleeves for mechanical fibre optic splices are
advertised as allowing connection and disconnection. In this way a mechanical
splice may be used in applications where the splice may be less permanent.
Fusion splices offer a lower level of loss and a high degree
of permanence. However they require the use of the expensive fusion splicing
equipment. In view of this they tend to be used more for the long high data rate
lines that are installed that are unlikely to be changed once installed.
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