Europe puts plastic optical fibre to work

17 Jun 2002

While Japan is the largest manufacturer of plastic optical fibre, it is Europe that is driving the development of new applications and testing standards. Nadya Anscombe reports.

From Opto & Laser Europe September 2001

Plastic optical fibre

Plastic optical fibre is one of those technologies that sounds really interesting but will never make it onto the market, right?

Wrong. Not many people realise that plastic optical fibre (POF) is already widely used in cars, CD players, industrial electronics, minidisc systems and PCs. There are also plans to use POF in sensors and to make photonic crystal fibres

The next few months will be an important time for the European POF industry: new European guidelines for the testing and measurement of POF will be introduced; the world's first dedicated POF applications centre (POFAC) opens officially in Nuremberg, Germany; BMW launches its new 7 Series, which features a record 100 m of POF; and the POF 2001 conference takes place alongside the European Conference on Optical Communications in Amsterdam, the Netherlands.

Hans Poisel, director of POFAC, told OLE: "POF has been used in lighting for many years and in every CD player today there is a piece of POF. The people who believe that it is still a research project are right to a certain extent - research is being carried out, but then research is still being carried out into copper cables too. POF is used in many applications today and Europe is the largest market for the technology." POF has several advantages over glass fibre: it is much cheaper to install - a simple moulded plug is all that is required to align and connect plastic fibres; well established production techniques are used in its manufacture; it is more flexible; it can be produced in greater thicknesses, making it more straightforward to couple light into the fibre and make robust low-loss connections to transmission equipment; and it is not as sensitive to vibrations.

POF in cars

It is this last advantage that has driven POF applications in cars. All Mercedes cars, from the S class to the A class, use POF to communicate information between the radio, the navigation system, the CD player and the mobile phone system. The total amount of POF used is approximately 12 m.

BMW has gone one step further than Daimler Chrysler (maker of the Mercedes). BMW is for the first time using POF to connect not only the multimedia systems in its new 7 Series, but also the safety features.

BMW 7 Series

Alfred Broede, spokesman for BMW, told OLE: "We are using two bus systems, one for all multimedia applications and one for connecting all of the sensors in the safety devices. There is no price advantage for using POF instead of copper. The advantages for us are high data rates, reduced weight, less packaging and no problems with electromagnetic interference."

The multimedia bus system MOST (24 Mbit/s) has been developed and used by several car manufacturers, whereas the safety bus system ISIS (10 Mbit/s) has been developed by BMW in-house.

It is the German automotive industry that has not only driven the development of applications for POF, but has also set the test and measurement standards for the fibre.

Olaf Ziemann, scientific director of POFAC, is part of a working group that is setting up guidelines for the testing of POF for the German Association of Engineers (VDI) and the German Association of Electronics Engineers (VDE). Ziemann told OLE: "These guidelines are important. For example, there is no standard way of determining the attenuation of POF. We sent pieces of POF to 10 institutes and asked them to measure this. We received 10 different results, which varied by more than 50%." Japanese standards do exist, but they have been deemed insufficient by the European community. Ziemann said: "The Japanese-industry standards describe only one type of POF, with a standard numerical aperture of 0.5, and only one wavelength [650 nm]. Also, the standard does not mention different stimulation conditions or that you must generate an equilibrium mode distribution in POF to achieve reproducible results."

Many established test methods cannot be used on POF. For example, optical time-domain reflectometry is a technique that is used for the determination of the location and power loss of bends, cuts and breaks in silica fibre. However, POF cannot be tested using this method because it exhibits Rayleigh scattering.

Ziemann said: "There is only one instrument on the market that is suitable for characterizing POF and this has been developed by a new Swiss start-up company called Luciol Instruments."

The guidelines that have been drawn up by VDI and VDE describe in detail how to measure the numerical aperture and attenuation, transmission and mechanical characteristics, and environmental and ageing characteristics of POF.

The first draft of the guidelines will be published in the autumn and these will be crucial to promoting international trade and eliminating misunderstandings. The following describes a selection of papers that are being presented at this month's POF 2001 conference in Amsterdam, the Netherlands.

For more information visit the organizer's Web site A large-core POF with an improved and well controlled luminance has been made by researchers at the University of Saint-Etienne in France. The group made a 10 mm diameter, 30 m long fibre and dispersed transparent microparticles into the fibre's polymer matrix to improve its light-scattering properties. The absorption loss of visible light induced by the particles was negligible, but light scattering was increased. A record transmission distance of nearly 1 km has been achieved by researchers at the Eindhoven University of Technology in the Netherlands and Asahi Glass in Japan using perfluorinated graded-index POF. The experiment was carried out using an 840 nm VCSEL at a bit rate of 1.25 Gbit/s - the same rate as that used for gigabit Ethernet applications. The key elements for this success, says the group, were an improved low-loss fibre launched with only a few modes; a VCSEL with a small spectral width and a bandwidth of 2 GHz; and a silicon avalanche photodiode with a large active area. A group of researchers from the University of Limerick, Ireland, the University of Twente, the Netherlands and the University of Liverpool in the UK has found that POF-based sensors can be used for high-energy electron-beam positioning in free-electron lasers. POF sensors can be used because they have good electrical isolation and electromagnetic immunity. The group found that, by using a sensor design that features an epoxy and an aluminium coating, the component was able to withstand the bombardment from the high-energy electrons. Researchers from the Daimler Chrysler research centre in Germany have integrated POF into flat flexible cables for automotive applications and connection with flat printed-circuit boards. Their designs allow POF and copper fibres to be integrated without the need for special precautions.

The researchers have also shown that the production process used to integrate naked POF into the flat flexible cable does not affect the optical properties of the fibre. POF-based photonic-crystal fibres more than 50 m long have been made by researchers at the Kwangju Institute of Science and Technology in Korea. The structure of the fibre is the same as that of silica-based photonic crystal fibre (PCF), with air holes running along its entire length. Its production process is also similar. The fibre is drawn from a 50 mm-diameter PMMA preform, and its diameter is controlled by the drawing speed.

This method gave fibre diameters of between 100 and 1000 µm and core diameters of between 20 and 100 µm. The researchers say that the structure of the polymer PCF remained constant throughout its length and did not collapse - a problem that is often encountered with the stacking tube technique used to make glass PCF. Visit POF Applications Centre and Luciol Instruments