Plastic optic fibres

Plastic optic fibres are 1-millimetre diameter threads, similar to a guitar string. Nowadays, optic fibres are used in the home, cars, trains and aeroplanes, for example.

How is the information transmitted?

At one end of the fibre the light source, either LED or laser, is attached. Lasers are faster and, thereby, can send greater quantities of information; but they are also more expensive.

Light emanating from the source will immediately propagate through the fibre and arrive at the other end where a receptor system is installed. Here this signal is interpreted as a 1. But, if the light beam is interrupted, the signal will not arrive at the receptor and, as a result, this will read 0. This is how images, texts and all kinds of digital information are transmitted, given that, in digital systems, information is codified by means of a binary system of ones and zeros.

Apart from transmitting information, optic fibres can also be used to make sensors. For example, in the automotive sector, they are regularly used in car safety systems such as indicating the need to change the engine oil.

The sensor immersed in the oil will be subjected to variations in the quantity of light transmitted depending on the increase in impurities in the oil. Thus, the moment there is no longer sufficient light getting to the receptor is when this sends a signal to change the oil. This is just one example of the use of an optic fibre sensor, but there are many more.

All advantages

Apart from having an infinity of applications, plastic optic fibres have many advantages: they are cheap, being made of metacrylate, a very common plastic. The connectors required are also cheap and simple. The fibres are light, a car weighing up to 50 kg less if the wiring is carried out with plastic fibres. And perhaps the most important advantage: the transported signal does not produce interference given that the electromagnetic fields and the rest of the electrical signals do not influence the plastic.

However, there are disadvantages also. They are not suitable over large distances as they produce losses in the transmission of light. As a consequence, the optic fibres have a maximum of one kilometre length; for longer distances glass optic fibres are used. Moreover, they cannot operate at temperatures greater than 80º C, given that the plastic melts and the fibre loses the transparency necessary for correctly transmitting the light. Finally, if there are many buckles or curves along the way, there are also losses of light at these points.

Research at the EHU (the University of the Basque Country)

At the School of Engineering in Bilbao a research team is working on plastic optic fibres. In their research they have designed software that simulates the way in which light is propagated down a plastic optic fibre, a tool that a number of companies already use. Moreover, they design and develop new devices or sensors based on plastic optic fibres. Finally, it should be pointed out that they have also worked with the automotive sector, analysing, above all, the losses produced in the wiring in the car at kinks and corners and, in this way, to be able to adapt the topology and minimise signal losses.