EuroWire November 2014

News Technology

Undersea fibre optic cables linking the world

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 : www.sikora.net

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.

▲ ▲ The Fiber Laser 6003 measures the diameter of the optical fibre in the drawing tower

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

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November 2014