Bigger, better invisibility cloak appears

You'd need around 100,000 waveguides to cloak the average mane
You'd need around 100,000 waveguides to cloak the average mane

Can an invisibility cloak ever be something you've seen before? If so, previous versions have been hyped up but have delivered little in the way of actually being able to sneak into the cinema for nothing.

A new tapered optical waveguide from Professor Vladimir Shalaev at Purdue University in Indiana seems more promising, being the first cloak to work across the entire visible spectrum rather than just a single frequency of light.

And where previous cloaking designs have used exotic metamaterials, requiring complex nanofabrication, the new design is a far simpler device similar to those used in fibre-optic communications.

Hide single hairs from view!

The research team used their specially tapered waveguide to cloak an area 100 times larger than the wavelengths of light shined by a laser into the device. Previous experiments with metamaterials have been limited to cloaking regions only a few times larger than the wavelengths of visible light.

The device is formed by two gold-coated surfaces, one a curved lens and the other a flat sheet. The researchers cloaked an object about 50 microns in diameter, or roughly the width of a human hair, in the center of the waveguide.

"Instead of being reflected as normally would happen, the light flows around the object and shows up on the other side, like water flowing around a stone," Shalaev said.

The research is part of transformation optics, which may usher in a host of radical advances, including cloaking; powerful hyperlenses resulting in microscopes 10 times more powerful than today's; computers and consumer electronics that use light instead of electronic signals to process information; advanced sensors; and more efficient solar collectors.

Researchers do not know of any fundamental limit to the size of objects that could be cloaked with the waveguide, but additional work will be needed to further develop the technique.