A nano-sized bar of glass encased in silver allows visible light to pass through at near infinite speed. The technique may spur advances in optical computing.
Metamaterials are synthetic materials with properties not found in nature. Metal and glass have been combined in previous metamaterials to bend light backwards or to make invisibility cloaks. These materials achieve their bizarre effects by manipulating the refractive index, a measure of how much a substance alters light鈥檚 course and speed.
In a vacuum the refractive index is 1, and the speed of light cannot break Einstein鈥檚 universal limit of 300,000 kilometres per second. Normal materials have positive indexes, and they transmit at the speed of light in a vacuum divided by their refractive index. Ordinary glass, for instance, has an index of about 1.5, so light moves through it at about 200,000 kilometres per second.
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No threat to Einstein
The new material contains a nano-scale structure that guides light waves through the metal-coated glass. It is the first with a refractive index below 0.1, which means that light passes through it at almost infinite speed, says Albert Polman at the FOM Institute AMOLF in Amsterdam, the Netherlands. But the speed of light has not, technically, been broken. The wave is moving quickly, but its 鈥済roup velocity鈥� 鈥� the speed at which information is travelling 鈥� is near zero.
As a feat of pure research, Polman鈥檚 group did a great job in demonstrating the exotic features of low-index materials, says , who was not involved in the work.
Practical applications might also be in the offing. The metal component that reduces the refractive index also increases absorption, so the light can鈥檛 travel far, says Polman. Still, the material could be used to transmit light rapidly over the very short distances in optical integrated circuits, he says.
Journal reference: Physical Review Letters,
