A Practical Introduction to
Fibre Optics
November 2014
Colin G4GBP
The history of fibres
• There are references going right back to the
Roman times of glass being pulled into strands
and being used as ‘light pipes’. Our real
interest starts in about 1970 when Corning
started doping silica glass and Bell Labs
demonstrating that a semi-conductor laser
could be used to send signals down the fibres
with very low losses. The first practical use of
fibre optic cables was by Dorset Police in 1975
How are fibre optic cables made?
From very pure glass.
1 Making a preform glass cylinder (seed)
2 Drawing the fibres from the cylinder
3 Testing the fibres
Drawing fibres from the seed
Nn
The ‘seed’ gets heated to 1900⁰C
The first glob drops by gravity
and forms a thread
Then it is drawn down by tractor
Heat and micrometer control dia.
Feed rate between 10-20m/s
About 1.5 miles fed on to drum
Sizes of fibres
The normal fibre optic cables that are in
common use today are shown below:
62.5µm known as OM1
50µm known as OM2
9µm known as OS1
OM1, OM2 & OS1 – why?
OM1 with its larger internal core diameter
allows the light to scatter more. Narrowing the
diameter of the core reduces this effect. This
allows greater distances and higher data rates
I don’t see the light…
Visible Red light has a nominal wavelength of
650nm
Fibres use 850nm for short distances using OM1
& 2 whereas OS1 uses the lower wavelength
1300-1550 for greater distances/higher data
rates
The Fusion Splicer
Here is a picture of
my fusion splicer.
Behind the black
Hood is an LCD screen
In front is the fuser
mechanism itself.
Splicing step 1
To join fibre optic cables we need to strip the
outer ‘buffer layer’ off.
Then we need to cut or
cleave the core & cladding.
This must be a ‘perfect’
Cleave so that the two
joints can be spliced together with the fusion
splicer.
Splicing step 2
The ends are ‘cleaved’
This is done by putting a
very small ‘nick’ in the
glass and then ‘breaking’
the glass fibre.
Slicing step 3
Each ‘cleaved’ end is laid
into the fusion splicer and
held down in precise ‘V’
blocks.
Splicing step 4
The fusion slicer has
two sets of cameras,
Servos adjust the jaws
so that the fibres are in
exact alignment before
applying a carefully
metered arc to weld the fibres. It measures the
losses across the joint and tests for tensile strength.
Splicing step 4
The last stage is to protect the joint with a heat
shrinked sleeve. The sleeve has a metal bar
through it to stop it bending.
Job done!