The ability to send multiple signals through a single channel, called multiplexing, is a fundamental feature of any voice or data communication system. Terahertz networks, which would operate at much higher frequencies than today’s microwave networks, offer a much larger capacity to carry data, however research is still underway in trying to make terahertz communication practical.
In their demonstration, the Brown researchers were able to transmit two separate real-time video signals through a terahertz multiplexer at a data rate of more than 50 gigabits per second – 100 times faster than today’s fastest cellular data networks.
“We showed that we can transmit separate data streams on terahertz waves at very high speeds and with very low error rates,” says Daniel Mittleman, a professor at Brown University’s School of Engineering and a corresponding author of a paper on the research. “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.”
The multiplexer/demultiplexer that the researchers developed uses two parallel metal plates – one of which has a slit cut into it – to form a waveguide. When terahertz waves travel through the waveguide, some of the radiation leaks out of the slit – the angle at which it escapes being dependent on 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,” says Mittleman. “Each of those frequencies leaks out of the slit at a different angle, separating the data streams; that’s demultiplexing.”
The researchers first published their waveguide idea as a proof of concept in 2015. This latest work tested the device with real data.
The researchers encoded two high-definition television broadcasts onto terahertz waves of two different frequencies – 264.7 GHz and 322.5 GHz – and then beamed both frequencies together into the multiplexer system, with a television receiver set to detect the signals as they emerged. When the receiver was aligned to the angle from which 264.7 GHz waves were emitted, the researchers saw the first channel; when it was aligned with 322.5 GHz, they saw the second.
According to the researchers, the transmissions were error-free up to 10 gigabits per second – 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 error correction techniques commonly used in today’s communications networks.
The researchers plan to continue developing their multiplexer and other terahertz components. They 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 says. “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.”
Terahertz transmitter promises wireless links 10x faster than 5G
Analog digital conversion for terahertz data
Terahertz tech moves from tabletop to microchip
Researchers create energy-efficient, tunable terarhertz source