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 demonstrati ID: 508195
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Slide1
A Practical Introduction to Fibre Optics
November 2014
Colin G4GBPSlide2
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 1975Slide3
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 fibresSlide4
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 drumSlide5
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 OS1Slide6
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 ratesSlide7
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 ratesSlide8
The Fusion Splicer
Here is a picture of
m
y fusion splicer.
Behind the black
Hood is an LCD screen
In front is the fuser
mechanism itself.Slide9
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
j
oints can be spliced together with the fusion splicer.Slide10
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.Slide11
Slicing step 3
Each ‘cleaved’ end is laid
i
nto the fusion splicer and
h
eld down in precise ‘V’
b
locks.Slide12
Splicing step 4
The fusion slicer has
t
wo sets of cameras,
Servos adjust the jaws
s
o that the fibres are in
exact alignment beforeapplying a carefully metered arc to weld the fibres. It measures the losses across the joint and tests for tensile strength.Slide13
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!