First Data Transmission With Terahertz Multiplexer

A research team have demonstrated the first data transmission through a terahertz multiplexer. (Source: Mittleman lab, Brown U. / Ducournau Lab, CNRS, U. Lille)

Multi­plexing is a fundamental feature of any voice or data communi­cation system. An inter­national research team has demonstrated for the first time a method for multi­plexing data carried on terahertz waves, high-frequency radiation that may enable the next gene­ration of ultra-high bandwidth wireless networks. The researchers report the trans­mission of two real-time video signals through a terahertz multiplexer at an aggregate data rate of 50 gigabits per second, approxi­mately 100 times the optimal data rate of today’s fastest cellular network.

“We showed that we can transmit separate data streams on tera­hertz waves at very high speeds and with very low error rates,” said Daniel Mittle­man, a professor in Brown’s School of Engi­neering. “This is the first time anybody has charac­terized a terahertz multi­plexing system using actual data, and our results show that our approach could be viable in future terahertz wireless networks.” Current voice and data networks use microwaves to carry signals wirelessly. But the demand for data trans­mission is quickly becoming more than microwave networks can handle. Tera­hertz waves have higher frequencies than micro­waves and therefore a much larger capacity to carry data. However, scientists have only just begun experi­menting with tera­hertz fre­quencies, and many of the basic components necessary for terahertz communi­cation don’t exist yet.

A system for multi­plexing and demulti­plexing is one of those basic components. This mux/demux approach Mittle­man and his colleagues developed uses two metal plates placed parallel to each other to form a waveguide. One of the plates has a slit cut into it. When terahertz waves travel through the waveguide, some of the radia­tion leaks out of the slit. The angle at which radiation beams escape is dependent upon the frequency of the wave. “We can put several waves at several different fre­quencies – each of them carrying a data stream – into the waveguide, and they won’t interfere with each other because they’re different frequencies; that’s multi­plexing,” Mittleman said. “Each of those frequencies leaks out of the slit at a different angle, separating the data streams; that’s demulti­plexing.”

Because of the nature of terahertz waves, signals in terahertz communi­cations networks will propagate as direc­tional beams, not omnidi­rectional broadcasts like in existing wireless systems. This direc­tional relationship between propa­gation angle and frequency is the key to enabling mux/demux in terahertz systems. A user at a parti­cular location (and therefore at a particular angle from the multi­plexing system) will communi­cate on a parti­cular frequency.

Working with Guillaume Ducournau at Institut d’Elec­tronique de Micro­électronique et de Nano­technologie, CNRS/University of Lille, in France, the researchers encoded two high-defi­nition television broadcasts onto terahertz waves of two different fre­quencies: 264.7 GHz and 322.5 GHz. They then beamed both fre­quencies together into the multi­plexer system, with a tele­vision receiver set to detect the signals as they emerged from the device. When the researchers aligned their receiver to the angle from which 264.7 GHz waves were emitted, they saw the first channel. When they aligned with 322.5 GHz, they saw the second.

Further experi­ments showed that trans­missions were error-free up to 10 gigabits per second, which is much faster than today’s standard Wi-Fi speeds. Error rates increased somewhat when the speed was boosted to 50 gigabits per second – 25 gigabits per channel, but were still well within the range that can be fixed using forward error correction, which is commonly used in today’s communi­cations networks.

The researchers plan to continue developing this and other tera­hertz components. Mittleman recently received a license from the FCC to perform outdoor tests at terahertz frequencies on the Brown Uni­versity campus. “We think that we have the highest-frequency license currently issued by the FCC, and we hope it’s a sign that the agency is starting to think seriously about tera­hertz communi­cation,” Mittleman said. “Companies are going to be reluctant to develop tera­hertz techno­logies until there’s a serious effort by regu­lators to allocate frequency bands for specific uses, so this is a step in the right direction.” (Source: Brown U.)

Reference: J. Ma et al.: Frequency-division multiplexer and demultiplexer for terahertz wireless links, Nat. Commun., in press (2017) • R. Mendis et al.: Artificial dielectric polarizing-beamsplitter and isolator for the terahertz region, Sci. Rep. 7, 5909, online:; DOI: 10.1038/s41598-017-06297-7

Link: Mittleman Lab, School of Engineering, Brown University, Providence, USA

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