Shrimp eyes tuned to polarised light

Scientists have discovered that the eyes of an Australian crustacean are highly efficient at detecting polarised light.

The research, published in today's edition of Nature Photonics, could inspire the next generation of liquid crystal displays and DVD devices.

Marine biologist Professor Justin Marshall of the University of Queensland says mantis shrimps have eyes made up of hundred of individual compartments.

He says each compartment has a photoreceptor in it, which he says detect visible light and turn it into a signal the brain can read.

But Marshall says mantis shrimp also have a special group of photoreceptors, known as R8 cells, which can also detect UV and polarised light.

Polarised light is light that is travelling in one plane, as compared to non-polarised light, like that from the Sun or a light bulb, which travels in all planes.

Marshall says polarised light comes in two forms, linear and circular.
Quarter-wave retarders

Linear polarised light vibrates, says Marshall, because humans don't have a polarising filter in their eyes, light travelling in multiple linear planes appears as glare.

"Polarised sunglasses cut down glare and allow us to see into water."

Marshall says, unlike most other animals, shrimp have sophisticated eyes they can turn linearly polarised light into circular polarised light and vice versa.

To do this, R8 photoreceptor cells act as quarter-wave retarders, which alters the plane of the polarisation as the light travels through it, he says.

"They do that in order for the cells beneath them to pick up circular polarised light - it's a co-operative filtering."

Marshall says quarter-wave retarders use the same process of turning linearly polarised light to circular polarised light as in CD and DVD players.

But he says these artificial devices are far less efficient than the shrimp's biological mechanism.

"We don't fully understand how they do it, but it's got to do with the structure of the R8 cells."


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