Sea mouse promises bright future

Shiny spines hide useful optical secrets

A humble marine worm with a talent for optical engineering may hold the clue to new communication technologies.

Little is known about the sea mouse but its spines are exciting physicists

Researchers in the UK and Australia said the technical wizardry of the lowly sea mouse could be copied to develop hi-tech photonic systems.

The sea mouse, or Aphrodita, has spines that normally appear deep red in colour. But when light falls on a spine perpendicular to its axis, stripes of different colours appear - strong blues and greens.

Writing in the journal Nature, the scientists, led by Ross McPhedran, from the University of Sydney in Australia, said: "The simple structure responsible for this effect is a remarkable example of photonic engineering by a living organism."

Hexagonal cylinders

Photonics is a branch of optics technology concerned with the control of photons, the elementary "packages" of light.

This effect is a remarkable example of photonic engineering by a living organism

The researchers investigated the sea mouse's photonic skills by mounting a spine in resin, slicing it into sections and examining it under an electron microscope.

They found that the spine was made up of numerous hexagonal cylinders, stacked in layers to form a crystal-like structure.

Each cylinder is just a fraction of the wavelength of light in diameter. The precise arrangement of the cylinders maximised reflectance around a narrow wave bandwidth, giving rise to the red colour.

Remarkably, the spines handle light with almost 100% efficiency.

Sea-floor life

The spines are made of protein and have a defensive role. Their colour acts as a warning to predators.

The high reflectance of the spines appears to be a product of habitat. The sea mouse exists from the ocean shallows to the abyssal depths, having been found at over 2,000 metres (6,560 feet) down.

The off-axis colours of blue and green replace the brilliant red

"Below a few hundred metres little light reaches the ocean floor, so for the spines to be effective they must make best use of every scrap of light available," said co-researcher Dr Andrew Parker of the University of Oxford. .

"Although the photonics of the spines are elegant and sophisticated, the spines themselves are simple.

"The mouse extrudes the spine material in the easiest way possible, much as a silk worm produces silk."

Because of their size and design, the hexagonal cylinders in the sea mouse spines perform much more efficiently than man-made optical fibres.

The researchers suggested that growing similar optical filters by molecular self-assembly might be possible:

"These structures may have application in photonic communications, where there is much interest in fabricating photonic crystal fibres with similar morphology."

Images courtesy of the University of Sydney, Australia