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Twisted Light Leads to 2.56 Tb/s Link

Orbital angular momentum boosts bandwidth

1 min read

Scientist in California and Israel say they've transmitted data through the air at a rate of 2.56 terabits per second using beams of "twisted light."

Such light poses the quantum property orbital angular momentum. As Alexander Hellemans explained in our May issue:

A photon can carry angular momentum just as a rotating body does and can even transfer the momentum to small particles, causing them to rotate. In theory, a photon can occupy any one of an infinite number of these quantum states, each associated with an integer value. These quantum states impart the... beam with a distribution of phases as it travels through space that gives the beam the shape of fusilli pasta (a helix).

Beams with different orbital angular momentum can be transmitted together on the same beam and then distinguished from each other at a receiver as if they had been sent on separate channels.

The communications technology could find a home in  satellite communication links, in short free-space optical links on earth (such as between buildings in a city), or maybe in  fiber optic cables (which the engineers say is their next step).

Orbital angular momentum has been studied intensively at optical wavelengths, but recently physicists have been trying to apply it to radio frequencies. Scientists in Europe claimed the first twisted RF communications earlier this year. But others question whether twisted RF is really different from other multiple-input-multiple-output radio techniques.

The research was publish on 24 June in Nature Photonics. The research team included Jian Wang, Jeng-Yuan Yang, Irfan M. Fazal, Nisar Ahmed, Yan Yan, Hao Huang, Yongxiong Ren, Allan Willner, and Yang Yue from the University of Southern California; Samuel Dolinar from NASA's Jet Propulsion Laboratory; and Moshe Tur from Tel Aviv University.

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Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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