News
Technology
November 2014
39
Whether sending emails, making phone
calls, watching TV or being online, it is
more than likely that the data is being
transferred via the international subsea
cable network. More than one million
kilometres of optical fibre cables are laid
in subsea cables in the oceans. Therefore,
subsea cables are the main carriers of the
international data transfer.
Subsea cables often lie in great water
depths of several thousand metres and
have to be especially robust as well as
built to a high quality standard, due to
the extensive technical maintenance.
Manufacturers of subsea cables have
extremely high demands on cable
production.
The aim is to produce long cable lengths
of high quality whenever possible in
one piece to avoid joints under water.
The demand on quality starts at the
production process of optical fibres, which
are built into a subsea cable for data
communication.
The continuous quality control of the
optical fibre is ensured during production
of the fibre in the drawing tower by the
use of innovative measuring and control
technologies at different production
stages.
At the beginning of the production of an
optical fibre is the preform. The preform
is created by means of chemical vapour
deposition and is available as a glass
rod with a diameter of 30-200mm. In
the first step, the preform is heated to a
temperature of 2,100°C in the drawing
tower. From the melted glass, the optical
fibre is drawn. At this point, the fibre
typically has a diameter of 125µm. After
cooling down, the optical fibre is coated
with an acrylate layer and hardened under
UV light. The coating protects the optical
fibre from mechanical damage. For further
processing, the fibres are wound onto
reels.
During the fibre drawing process, Sikora
measuring devices, in connection with
display and control devices, are used in
different positions to control the optical
fibre parameters.
Typically, a first gauge head, the Fiber Laser
6003, is installed below the draw furnace
to measure the diameter and position
of the uncoated fibre. The gauge head
calculates the tension from the vibration of
the fibre with Fast Fourier Transformation
(FFT). The single values of the fibre
position are graphically visualised by the
processor system Fiber Ecocontrol in the
form of a scatter plot and are available
by Ethernet. The laser measuring process
ensures a measuring accuracy of 0.05µm
at a repeatability of 0.02µm with 2,500
measurements per second.
A second laser-gauge head measures the
cold diameter of the optical fibre and the
spinning after cooling and before coating.
There is a risk during production of the
preform that air is trapped and which,
when drawn, becomes stretched air
pockets, so called airlines. These airlines
damage the quality of the optical fibre
and must be detected. This is why Sikora
has developed the Fiber Laser 6003 Airline.
With 2,500 measurements per second, this
device reliably detects airlines in the fibre
with a diameter from 0.5µm.
Before the acrylate layers are applied onto
the fibre, the exact measurement of the
optical fibre temperature is important.
Sikora offers the Fiber Laser 6003 Temp,
which measures precisely and reliably
the temperature of the optical fibre after
cooling. With the information about
the fibre temperature, the optical fibre
manufacturer can use the exact amount of
helium needed.
After the fibre has received the coating and
has gone through the UV drying process,
a further Fiber Laser 6003 measures the
diameter of the optical fibre. After the
coating, the diameter usually measures
about 250µm.
In addition to diameter measurement,
lump detectors are used for a continuous
quality control in drawing towers. The
3-axis Fiber Lump 6003 reliably measures
lumps with a length of 500µm. Due to
the growing quality requirements on the
optical fibre market, Sikora also offers the
Fiber Lump 6003 Micro. The device detects
faults from a length of 50µm on the optical
fibre surface up to 100 per cent. This
performance is achieved by the use of six
measuring axes.
With the display and control system Fiber
Ecocontrol, the data of the connected
gauge heads and lump detectors is
displayed graphically on a 15" TFT
monitor.
After the drawn fibre has been proof tested
and wound onto reels, the fibre is coloured
in a separate step and subsequently
processed to an optical cable in a loose
tubing or tight buffering line.
Sikora AG – Germany
Website
:
Undersea fibre optic cables linking the world
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The Fiber Laser 6003 measures the diameter of the
optical fibre in the drawing tower
