Physicists at Harvard University in the US have built a silicon waveguide that exhibits a refractive index of, or close to, zero when operating at near-infrared telecom wavelengths. The waveguide can transmit energy more efficiently than previous designs, offering potential applications in computing and communications.
Most materials have a refractive index of more than one, which means that they reduce both the speed and wavelength of light passing through them compared to light's passage in a vacuum. But a material with zero refractive index instead boosts the speed and wavelength of light to infinity, leaving it with a temporal but no spatial variation. (The effect does not contradict special relativity because it regards a wave's phase, which carries no information.)
Orad Reshef, who is now at the University of Ottawa, says he was inspired to investigate materials with zero refractive index because "zero was such an abstract concept". But, more practically, he says that zero-index materials might boost nonlinearity in light that is a long-standing and as-yet unfulfilled requirement for optical computers. This would mean one photon being able to dictate the behaviour of another, so enabling optical transistors and other types of switches.
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