New communication technologies could be the outcome of a new class of laser beam that scientists have recently created, which defy long-held laws of light physics. These new beams, dubbed “spacetime wave packets,” follow different rules of refraction than any known light beam.
The speed of light alters depending on the media it travels through; in denser materials, it slows down. For example, if you place a knife in a cup of water, the blade will appear to be sliced at the water’s surface. That happens because the light travels slower through the water than the air, and as the light rays enter the water, they bend. This spectacle is known as Snell’s Law.
Spacetime wave packets don’t follow this law of light, nor does it follow Fermat’s Principle, which states that light always takes the shortest possible route.
Ayman Abouraddy, the leading investigator of the study explained:
This new class of laser beams has unique properties that are not shared by common laser beams. Spacetime wave packets can be arranged to behave in the usual manner, to not change speed at all, or even to anomalously speed up in denser materials. As such, these pulses of light can arrive at different points in space at the same time.
The new laser beams have significant potential for optical communications technologies. The team explains how, by providing an example of a plane sending messages encoded in light to two submarines, with different distances from each other but at the same depth. In a normal situation, the message would arrive at the closer sub first, but with spacetime wave packets, the pulses could be circulated to reach both precisely at the same time.
The team used a device called spatial light modulator to control the speeds at which the peaks of the light pulses travel, rather than messing with the oscillations of the light waves themselves. This device works by reorganizing the energy of each pulse of light to interweave its properties in space and time.
Basanta Bhaduri, the study’s co-author, said:
Space-time refraction defies our expectations derived from Fermat’s principle and offers new opportunities for molding the flow of light and other wave phenomena.
The research was published on June 22 in the journal Nature Photonics.
