A striking demonstration of a means to boost the information-carrying capacity of radio waves has taken place across the lagoon in Venice, Italy.
The technique exploits what is called the “orbital angular momentum” of the waves – imparting them with a “twist”.
Varying this twist permits many data streams to fit in the frequency spread currently used for just one. …
In the simplest case, putting a twist on the waves is as easy as putting a twist into the dish that sends the signal. The team split one side of a standard satellite-type dish and separated the two resulting edges.
In this way, different points around the circumference of the beam have a different amount of “head start” relative to other points – if one could freeze and visualise the beam, it would look like a corkscrew.
In a highly publicised event in 2011, the team used a normal antenna and their modified antenna to send waves of 2.4 GHz – a band used by wi-fi – to send two audio signals within the bandwidth normally required by one. They repeated the experiment later with two television signals.
Crowds were treated to projections beamed onto the Palazzo Ducale explaining the experiment, and then a display of the message “signal received” when the experiment worked.
Prof Thide said that the public display – “in the style of (radio pioneer) Guglielmo Marconi… involving ordinary people in the experiment”, as the authors put it – was just putting into practice what he had believed since first publishing the idea in a 2007 Physical Review Letters article.
“For me it was obvious this would work,” he said. “Maxwell’s equations that govern electromagnetic fields are… the most well tested laws of physics that we have.
“We did this because other people wanted us to demonstrate it.”
Prof Thide and his colleagues are already in discussions with industry to develop a system that can transmit many more than two bands of different orbital angular momentum.
The results could radically change just how much information and speed can be squeezed out of the crowded electromagnetic spectrum, applied to radio and television as well as wi-fi and perhaps even mobile phones.