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Sea sponge grows performance fiber

22 Aug 2003

Bell Labs researchers discover that optical fiber manufacturers could learn a thing or two from a deep-sea sponge.

A deep-sea sponge grows optical fibers that are tougher than those manufactured by man (Nature 424 899).

That’s according to Joanna Aizenberg and colleagues at Bell Labs in the US and Tel Aviv University in Israel, who have been studying the Euplectella sponge.

The skeleton of the sponge is constructed from amorphous, hydrated silica and it features a network of so-called ‘spicules’ that provide structural support. These spicules closely resemble optical fibers used in telecoms networks, with a high-refractive-index core and a low-index cladding. When Aizenberg coupled light into the sponge’s spicules, she found that it acted like a single- or few-mode waveguide.

However, the natural fiber has some advantages over its man-made counterparts. It is tougher than commercial fiber, which tends to fracture. The layers contained within the spicules’ structure are connected by organic molecules that provide an effective crack-arresting mechanism.

The spicules also grow in an ambient environment, rather than the high-temperature furnaces used to make optical fiber. This allows the structure to become doped with certain impurities that improve the fiber’s performance.

If fiber manufacturers could learn to imitate the sponge’s low-temperature construction, they would be able to dope fibers with useful species like sodium, calcium or magnesium. These dopants could be used to selectively increase the refractive index of the glass and improve the fiber’s light transmission, and Aizenberg says that the refractive index of the bio-fibers doped with sodium exceeds that of commercial vitreous fiber.

Exactly why the sponge has high-performance fiber remains a mystery. Aizenberg told Optics.org that the spicules might provide an intricate network of fibers to distribute bioluminescence emitted by other organisms living inside its ‘basket’ (see image).

“Such a fiber-optical lamp might attract micro-organisms, especially shrimp, to the filter-feeding sponge. It is potentially an ‘illuminated glasshouse’ of the deep,” she said.

Michael Hatcher is technology editor of Opto & Laser Europe magazine.

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