SAFETY inspectors are being downsized – in a good way. Tiny glass beads patrolling fibre-optic cables could keep an eye on the insides of nuclear reactors and other hazardous environments.

Fibre-optic cables may be best known for delivering your broadband connection, but they are also used as sensors, measuring things like cracks or chemical leaks that change the amount of light passing through them.

Philip Russell of the Max Planck Institute for the Science of Light in Erlangen, Germany, and his colleagues have taken this a step further with a new kind of hollow fibre. These fibres were originally designed to improve data transmission, but Russell realised the empty cores could also work as channels for microscopic glass particles.

The team used lasers to manoeuvre particles into the fibre. They then showed that a particle exposed to a varying electric field would oscillate inside the fibre, changing the amount of laser light the particle scattered. They used this to measure the strength of the electric field.

The team was also able to measure temperature variation by looking for changes in the speed at which the particle travelled down the fibre, which is determined by the viscosity of air, which in turn depends on temperature (Nature Photonics,

Particles prepared in different ways could measure other properties. Made from the right material, they could give off light in the presence of radiation, for example. This would be particularly useful in nuclear reactors.

“It’s an impressive piece of work,” says William MacPherson of Heriot-Watt University in Edinburgh, UK, who thinks the sensors could also be used to monitor complex scientific experiments. “It opens up an exciting possibility for making localised measurements that you can move around.”

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