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Fibre provides

David Robson examines how the fibre optics market has evolved to encompass much more than just the telecommunications industry

The collapse of the telecom industry was a dark period for many fibre optic suppliers. ‘We had a hard time there,’ says Rob Morris, director of marketing at Ocean Optics. ‘It probably eliminated some of the weaker players.’

Optical fibres were the basis of the industry, providing the data transfer links for high-speed communication. It took a while before

customers realised there was more to optical fibres than broadband internet, but fibre technology is now being used in cancer treatment, airline safety and industrial manufacturing. It has been a rocky road, but those that survived are stronger than ever before.

Science and medicine

The use of optical fibres to transmit images from the digestive system in keyhole surgery may be well known, but fibre optics are now allowing doctors to look under the skin of a patient without even cutting the skin.

The fibres are used to make an interferometer, in a method called optical coherence tomography that is already being used in ophthalmology to scan the retina. In the future, it could also be used for dentistry and cancer treatment. It can provide images of tissue millimetres under the skin, at micron resolution, by measuring the way different light beams interfere with one another.

‘This will be huge in years to come,’ predicts Paul Ellis, managing director of Sifam Fibre Optics. ‘It will be as prominent as MRI scanning.’

Another recent development in fibre technology has been the ability to produce fibres with varied numerical aperture, which in turn determines how much light the fibre material can carry. This has meant that much thinner, less obtrusive fibres can transmit enough energy for medical applications.

This is already providing greater comfort to prostate cancer patients who are treated with photodynamic therapy. The patient is injected with a drug that makes the tumour highly sensitive to light. The optical fibre then directs the light onto the sensitised tumour with high accuracy, destroying it in the process.

This treatment is far less invasive than other treatments, and is less likely to provoke side-effects such as sexual dysfunction. ‘These operations can even be performed with no overnight stay,’ says Cheryl Provost, scientific sales engineer at Ceramoptec, who provides the fibres for this application.

Provost says that these innovations are largely possible because the company has complete control over the production of the fibre. ‘Everything is done in-house, so we can put dopants into the fibre to change the numerical aperture.’

Medicine is not the only area of science to have benefited from developments in fibre technology. Ceramoptec’s products will be used on the JPL-NASA Mars Science Laboratory Rover, to be launched in 2009, to guide laser light that blasts Martian rocks apart. The fibres will also be used to transmit the resulting data back to a sensor that will analyse the composition of the rocks.

Scientists are also using a new kind of optical fibre to study the properties of light and different materials. Photonic crystal fibres have hollow cores, and have been used to reduce the pulse lengths of lasers and create very broad bandwidths of light.

Elliot Scientific doesn’t distribute the photonic crystal fibres, but it does provide the products that shine the light into the fibre. ‘There are several systems on the market, but we are seeing an increased interest in ours due to the high, long-term stability,’ says Mike Elliot, founder of Elliot Scientific. The light is directed very precisely, and its direction does not drift over time.

The Elliot/Martock MDE510 Fibre Launch System, used for research into photonic crystal fibres.

Photonic power modules

Fibre optics have traditionally been used to transmit optical signals through harsh environments, but recently suppliers have been looking into the possibility of using them to transfer enough energy to power small devices, in situations where copper wiring would not be feasible. The energy would first be converted into laser light, which is transferred across the fibres to a photodiode. This then converts the optical energy back to electrical energy with an efficiency of roughly 10 per cent.

That may not seem much, but it’s a huge step, and it would be enough to power current meters in electrical substations. If the current meter were powered by electricity, it would share a common ‘earth’ with the current it is supposed to be measuring. The optical fibres, however, are made from glass, so the meter is electrically isolated, making its measurements more reliable.

The devices that deliver this kind of energy are called photonic power modules, and they are causing quite a stir in a number of areas. ‘There’s a great interest outside the telecom industry,’ says David Welsh, sales director of Elliot Scientific. It would be an ideal way to power sensors in an MRI scanner, which also has a very strong electromagnetic field. They could also be used in military applications, as the electric field surrounding a cable can be detected more easily than an optical signal.

Optical sensors

Optical sensors, which rely solely on light to provide readings, are gaining popularity. Optical fibres are used to collect and transfer the signal because they can transmit light, even through environments that would otherwise be damaging to sensing equipment.

A more recent development has been to prime the tip of the fibres with a thin film of gel that fluoresces in the presence of certain chemicals. The fibre is split in two. One part transmits light from an LED to excite the fluorescence, and the other strand leads the output back to equipment that records the outcome.

An optical sensor from Ocean Optics measuring the reflection of seedlings.

Unlike electrical sensors, optical sensors don’t cause decay in the sample being studied, and they can be used in liquids as well as gases. Because the sensing head carries no current, they can even be used to measure the oxygen content in aeroplane fuel tanks, an idea that Ocean Optics is currently developing.

Optical fibres are also ideal for data transfer on aeroplanes because they weigh less than copper wires, and there has been talk of using them to provide in-flight video and internet access.

Sifam is currently working on this with a group of aerospace companies, including BAE and Airbus. ‘Professional people on aircraft are looking for the same connectivity as broadband at home. It’s the logical step for air travel. We’re building demonstrations at the moment, with the view to finalising an agreement,’ says Sifam’s Ellis.

Ellis says that the technology would have been commercially available sooner, but many people made the mistake of exploring multimode fibres, which don’t give as large a bandwidth as single-mode systems. They are also an attractive option to transfer the control signals on planes, because their low weight means less fuel will be consumed than with copper wires. ‘The current environmental concern pushed the use of optical fibres right up the agenda,’ says Ellis.

That may seem like coming back full circle to the original purpose of fibre lasers, data communication, but it is a mark of their versatility and robustness that they are finally being accepted in the conservative aerospace industry. With their low cost and increasing capacity to transfer energy as well as data signals, it may not be long until the optical fibre is as ubiquitous as the copper cable.