Contents I. Introduction
Due to the high volume of data used in many areas, the data processing is becoming increasingly important. For example, the small medical devices monitor patients vital signs and report suspicious changes. An enormous number of sensors are installed in production machines, turbines, vehicles or scientific equipment to determine the condition of the machine via hundreds of parameters or to provide a forecast of how the part or machine will behave in the future. The created data have to be transmitted error free over long distances. This requires a new technology, that can transfer an enormous amount of data fast and reliably. Here, the fiber optic cable offers a far better performance compared to the conventional copper cable. In terms of transmission speed and volume of data, the fiber optical transmission is superior. Furthermore, fiber optic cables are less susceptible to electromagnetic interference. The installation of fiber optic cables is also facilitated by their reduced weight compared to conventional cables. These advantages alone demonstrate the preferable use of the glass fiber in various technical areas. In general, only one electrical signal can be transmitted per cable in conventional data transmission. In optical data transmission, the multiple different optical signals can be transmitted simultaneously without interference. This process is called Wavelength Division Multiplexing (WDM). Here, several wavelengths carrying information are combined in one optical fiber and split apart again at the receiving end of the fiber. Each wavelength is then representing a separate transmitting channel.
