fibre Optic Splicing Methods
There are two main methods for splicing fibres together - Fusion Splicing & Mechanical Splicing. Mechanical splicing has - to our knowledge - rarely been used for splicing large fibre counts; instead its main use has been for temporary coonections or emergency repairs.
The main reasons for splicing fibres are
(1) To connect pre terminated tails to the ends of fibres.
(2) To Join cables.
(3) To join two fibres with a low loss joint.
(4) To repair damages cables.
For the sake of our discussion we shall - for now - discuss only fusion splicing.
Correct preperation of the fibres to be spliced is essential if a good, low loss connection is to be made.
Depending on what cable you have to work with, it is likely made up of most, if not all, the following parts:
(1) Core - Typically 8 (SingleMode), 50 or 62.5 (Both MultiMode) microns.
(2) Cladding - 125 microns.
(3) Primary Coating - 250 microns.
(4) Secondary Coating - 900 microns.
Before fusing the fibres together both lengths of fibre needs to be stripped down to the cladding at the ends. Tools are available to do this easily;
for example a "Miller Stripper" has a laser drilled hole drilled slightly larger than 125 microns to use for stripping primary coatings.
Once the fibres have been stripped it is neccessary to thoroughly - and carefully - clean the fibre ends, this is best done with
a degreasing solvent such as Isopropyl Alcohol (IPA). This is best done by applying IPA to a lint free tissue and gently pulling the fibre
through the tissue twice; holding the tissue sides (in a V shape) with your spare thumb and forefinger.
For best results when splicing fibres together it is essential that the ends of the fibres are cut squarely. This is known
as cleaving and is best done with a good quality cleaver bought specially for the purpose. Cleavers can be quite expensive - in excess of £1,000 - but should
be able to produce a fibre end that is clean and flat with no hackle (rough edges).
Fusion Splicing Procedure
The fusion splicing procedure differs very little between splicers and generally comprises of the following 9 steps:
(1) fibre Preperation
Its always best to develop a routine when splicing fibres and one of the first things which you should remember to do is feed a splice protection sleeve (strengthened plastic tube)
over one of the fibres. The ends of the fibres should be stripped (as outlined above) and cleaned. Enough of the fibre should be stripped to enable the end (after cleaving)
to fit into the fusion splicer moutning.
(2) fibre Cleaving
The desired low loss splices are hard to achieve without fibres that have been well cleaved leaving square ends. This is even more so with Singlemode fibres.
(3) Mounting the fibres
The fibres are clamped into place in the fusion splicer. Fusion splicers often use two clamps per fibre, one clamp over the coating, the other over the bare fibre.
(4) Coarse Alignment
The ends of the fibres are brough close together and alligned between the splicers electrodes. In modern splicers this is done automatically by the splicer
with an image of the fibre ends displayed on a screen; older splicers required manual allignment.
(5) fibre Cleaning Arc
A short discharge from the splicers elctrodes is used to burn off any dust particles or other dirt from the fibre ends.
(6) Fine Alignment
The ends of the fibres are brought together. There are a number of methods for passive and active alignment, modern splicers do the alignment automatically.
(7) Main Fuse
At this stage an electric arc (from the splicers electrodes) - which can often be programmed within the splicer for differing fibre cables - is created
across the ends of the fibre to melt them. The fibres are pushed together so that they can fuse together. A number of problems can occur during the main fuse which is why the next step is...
(8) Inspection & Test
Visual inspection of the fuseion point through a microscope or via the splicers own display on modern devices will give a good
idea as to the success of the splice. A number of modern splicers will give an estimation of the splice loss, however it must be rememberd this is only an
estimation. Prior to removing the fibres from the splicer, the machine may put some strain onto the splice to ensure a good pysical joint has been made.
(9) Splice Protection
Once the splice has been completed the bare fibres will need protecting, hence the splice protection sleeve in step (1). The splice protection sleeve - which is
just a tube of heat shrink with a stregthening member incorporated - is pulled over the splice and the assembly is placed into the oven
which is part of the splicing machine.