Italian scientists have demonstrated the principle by transmitting two radio waves at the same frequency — but different levels of twist — over a distance of 400m, then picking up the two separate channels.
‘It’s independent of polarisation — a completely different physical state — you can handle both the two quantities independently,’ lead researcher Fabrizio Tamburini told The Engineer. ‘The idea was why don’t we use this new degree of freedom to transmit information, like Marconi did with the band division of the electromagnetic spectrum.’
With the introduction of mobile smartphones, wireless Internet and digital TVs the number of radio frequency bands available to broadcast information is increasingly limited.
Tamburini took advantage of the fact that a wave can twist about its axis a certain number of times in either a clockwise or anti-clockwise direction, meaning there are several configurations that it can adopt. The researchers used a special twisted parabolic antenna to transmit two radio waves in the 2.4GHz band over a distance of 442m, where the separate channels were detected.
In theory, 11 channels can be generated with one frequency band using five orbital angular momentum states, from –5 (counter-clockwise) up to 5 (clockwise), including untwisted waves. The use of multiplexing, as in digital TV signals, could increase this to 55 channels in the same frequency band.
‘We are trying to set up a new type of wireless communication — it is not difficult to build up Wi-fi with this technology and you can improve security and connect a lot of computers with the same router, and increase the local bandwidth,’ Tamburini said.