EuroWire January 2018
Measuring devices for quality control of optical fibres in the drawing tower for a perfect fit in subsea cables By Katja Giersch, Sikora AG, Bremen, Germany
Introduction Recent studies show a growth of undersea optical fibre connections for the future. “Optical fibre is considered to be a good option to carry higher data rates over longer distances than copper cables. By 2020, an increase in subsea processing will generate more data, which will make the high bandwidth and longer transmission distances of optical fibres more attractive,” said ResearchandMarkets in its report on ‘Global Fibre Optic Connectors Market 2016-2020’.  We are currently observing two developments in manufacturing optical fibres. On one hand, there are countries such as China and the USA advancing further into the optical fibre market as copper cables are exchanged by optical fibres to meet the increasing demand for data transfer of more than one terabit per second. These countries have a backlog for drawing towers and are investing in new lines. are manufacturers who have been producing high-quality optical fibres for many years, but who cannot keep up with the speed of modern lines. These run the optical fibre at 1,200m/min whereas state-of-the-art towers achieve 3,000m/min. Measuring devices for quality control in the drawing tower For both applications, independent of the drawing speed, there are technologies On the other hand, there
available for measuring and controlling optical fibre parameters online in the drawing tower. Continuous quality control in the drawing tower is essential to ensure high-quality optical fibres for attaining a transfer of data over long distances without losses. In addition, quality plays an important role as drawn optical fibres are further processed to optical cables before they are installed, for example, in a subsea cable. This requires the compliance with optical fibre specifications to perfectly fit into the final application (subsea cable) and to ensure durability. Today, quality control of optical fibres takes place in the drawing tower by using 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 manufactured by means of chemical vapour deposition and is available as a glass rod with a diameter of 30–200mm. In the first step of fibre production, the preform is heated up in an inductive furnace to a temperature of 2,100°C. A new technology developed by Sikora, based on millimetre waves, can not only help to measure the diameter and the position of the remaining preform above the furnace, but also has the potential to distinguish differently doped glasses. 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 that is hardened under UV light.
The coating protects the optical fibre from mechanical damage and allows the fibre to be bent. For further processing, the fibres are wound onto reels. Typically, a first gauge head based on laser technology 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 a processor system in the form of a scatter plot and are available by Ethernet. ▲ ▲ At different positions in the drawing tower, Sikora online measuring devices are used for quality control and process optimisation
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