Two years ago I reported on 'Twisted wave' technology demonstrated in Venice. That demonstration showed the transmission of two microwave signals on one frequency over the same path using special antennas by using different orbital angular momentum states.
Researchers at the USC Viterbi School of Engineering appear to be doing something similar. Two years ago Prof. Alan E. Willner, Associate Director for the Center for Photonics Technology at USC, lead a team that twisted light beams to transmit data at 2.56 terabits per second. Recently the researchers have applied the technology to radio frequencies and were able to reach a data rate of 32 gigabits per seconds. This wasn't a long distance link–only 2.5 meters, free-space, in a basement lab at USC, but future research will focus on attempting to extend the transmission's range and capabilities.
Each beam, with its own independent data stream, was passed through a “spiral phase plate” that twisted it into a unique and orthogonal DNA-like helical shape. Eight of these 28 GHz signals use the same spectrum and same aperture but a different twist were combined. At the receive end, the beams are untwisted and the different data streams recovered.
Willner said, “Not only is this a way to transmit multiple spatially collocated radio data streams through a single aperture, it is also one of the fastest data transmission via radio waves that has been demonstrated.”
Andy Molisch of USC Viterbi commented, “This technology could have very important applications in ultra-high-speed links for the wireless 'backhaul' that connects base stations of next-generation cellular systems.” Molisch focuses on wireless systems and co-designed and co-supervised the study with Willner.
The work is detailed in a Nature Communications article, High-capacity millimetre-wave communications with orbital angular momentum multiplexing (opens in new tab) by co-lead authors Yan Yan and Guodong Xie, two graduate students at USC Viterbi and contributions from USC, the University of Glasgow, and Tel Aviv University. There is no charge for this detailed and well-illustrated article.
I wonder how long it will be until we see this technology being used to expand capacity in fixed links? I did not see any mention of non-line-sight paths or the size of antennas required for reception, so it isn't if OAM will work for portable devices.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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