MOZART and Schr枚dinger flew through the air over Vienna recently. Their digital images were encoded in twisted green light, marking an important step towards long-distance communication in free space.
Light offers the best way to communicate between Earth and orbiting satellites, but atmospheric turbulence can destroy the signal. Polarised light is resistant to the effects of turbulence, but polarised photons can carry only one bit of information apiece. So researchers have looked for other properties of light that could boost the bit rate.
One solution is twisted light, in which the wavefront of light spirals around a central axis as it travels. There is no limit to the number of twists for each photon, so they can theoretically store boundless amounts of information. Now, Mario Krenn, and their colleagues at the University of Vienna in Austria have transmitted photons with four levels of twists, giving them the ability to transmit four bits of information.
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Erwin Schr枚dinger, before and after his twisted flight (Image: Mario Krenn)
After digitising images of Mozart, Schr枚dinger and physicist Ludwig Boltzmann, the team encoded the data in twisted green laser light. Then they transmitted the beam from the top of a radar tower to a receiver 3 kilometres away 鈥� a record for twisted light transmission in the open air 鈥� where software read the patterns of light and decoded the images ().
鈥淚t鈥檚 a huge technological achievement,鈥� says , who studies twisted light at Heriot-Watt University in Edinburgh, UK. 鈥淚t鈥檚 really amazing that they were able to transmit these quite faithful images across what鈥檚 quite a long free-space distance.鈥�
聯It鈥檚 really amazing that they were able to send quite faithful images of Mozart and Schr枚dinger聰
The effective thickness of Earth鈥檚 atmosphere is only about 6 kilometres, so the demonstration is a big step on the way to using twisted light to communicate with satellites.
This article appeared in print under the headline 鈥淭wisted light transmits over record distance鈥�
