Optical fibres in deep-sea sponges

Scientists from Lucent Technologies’ Bell Labs have found that a deep-sea sponge contains optical fibre that is remarkably similar to the optical fibre found in today’s state-of-the-art telecommunications networks.

The deep-sea sponge’s glass fibre, which developed through the course of evolution, may possess certain technological advantages over industrial optical fibre, the scientists reported in the August 21 issue of the journal Nature.

‘We believe this novel biological optical fire may shed light upon new bio-inspired processes that may lead to better fibre optic materials and networks,’ said Joanna Aizenberg, the Bell Labs materials scientist who led the research team. ‘Mother Nature’s ability to perfect materials is amazing, and the more we study biological organisms, the more we realise how much we can learn from them.’

The sponge in the study, Euplectella, lives in the depths of the ocean in the tropics and grows to about half a foot in length. Commonly known as the Venus Flower Basket, it has an intricate cylindrical mesh-like skeleton of glassy silica and a pair of mating shrimp often lives inside it. At the base of the sponge’s skeleton is a tuft of fibres that extends outward like an inverted crown. Typically, these fibres are between two and seven inches long and about the thickness of a human hair.

The Bell Labs team found that each of the sponge’s fibre is composed of distinct layers with different optical properties. Concentric silica cylinders with high organic content surround an inner core of high-purity silica glass, a structure similar to industrial optical fibre, in which layers of glass cladding surround a glass core of slightly different composition. The researchers found during experiments that the biological fibres of the sponge conducted light when illuminated, and used the same optical principles that modern engineers have used to design industrial optical fibre.

‘These biological fibres bear a striking resemblance to commercial telecommunications fibres, as they use the same material and have similar dimensions,’ said Aizenberg.

Though these natural bio-optical fibres do not have the superbly high transparency needed for modern telecommunication networks, the Bell Labs researchers found that they do have a big advantage in that they are extremely resilient to cracks and breakage. Although extremely reliable, one of the main causes for outages in commercial optical fibre is fracture resulting from crack growth within the fibre. Infrequent as an outage is, when it occurs, replacing the fibre is often a costly, labour-intensive proposition, and scientists have sought to make fibre that is less susceptible to this problem.

The sponge’s solution is to use an organic sheath to cover the biological fibre, Aizenberg and her colleagues discovered. ‘These bio-optical fibres are extremely tough,’ she said. ‘You could tie them in tight knots and, unlike commercial fibre, they would still not crack. Maybe we can learn how to improve on existing commercial fibre from studying these fibers of the Venus Flower Basket,’ she said.

Another advantage of the fibres is that they are formed by chemical deposition at the temperature of seawater. Commercial optical fibre is produced with the help of a high-temperature furnace and expensive equipment. Aizenberg said, ‘If we can learn from nature, there may be an alternative way to manufacture fibre in the future.’

Should scientists succeed in emulating these natural processes, they may also help reduce the cost of producing optical fibre. ‘This is a good example where Mother Nature can help teach us about engineering materials,’ said Cherry Murray, senior vice president of physical sciences research at Bell Labs.

‘In this case, a relatively simple organism has a solution to a very complex problem in integrated optics and materials design. By studying the Venus Flower Basket, we are learning about low-cost ways of forming complex optical materials at low temperatures. While many years away from being applied to commercial use, this understanding could be very important in reducing the cost and improving the reliability of future optical and telecommunications equipment.’

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