4-channel Silicon Multiplexer to Advance Terahertz-Based Communications

An ultra-small silicon chip called a multiplexer is poised to increase data processing speeds and the next generation of communications — 6G and beyond — as a result. The chip, developed by researchers from Osaka University and the University of Adelaide, is made from pure silicon and manages terahertz waves in the 300 GHz band.

According to associate professor Withawat Withayachumnankul from the University of Adelaide, a multiplexer, which is used to split and join signals, is critical for dividing information into manageable chunks that can be more easily processed to speed up transmission from one device to another.

“Up until now, compact and practical multiplexers have not been developed for the terahertz range. The new terahertz multiplexers, which are economical to manufacture, will be extremely useful for ultra-broadband wireless communications,” Withayachumnankul said. “The shape of the chips we have developed is the key to combining and splitting channels so that more data can be processed more rapidly. Simplicity is its beauty.”

Experimentation with the multiplexer, showing connection to external systems. The multiplexer does not have any form of supporting substrate. Courtesy of the University of Adelaide and Osaka University.

Terahertz waves are a portion of the electromagnetic spectrum that has a raw spectral bandwidth far broader than that of conventional microwave-based wireless communications. The terahertz multiplexers the team developed owe their ultra-compact form and efficiency to a novel optical tunneling process.

“A typical four-channel optical multiplexer might span more than 2000 wavelengths. This would be about two meters in length in the 300-GHz band,” said lead author Daniel Headland of the University of Osaka. “Our device is merely 25 wavelengths across, which offers dramatic size reduction by a factor of 6000.”

The multiplexer covers a spectral bandwidth that is over 30× the total spectrum allocated in Japan for 4G/LTE and 5G combined. As bandwidth is related to data rate, ultrahigh-speed digital transmission is possible with the new multiplexer.

“Our four-channel multiplexer can potentially support aggregate data rate of 48 Gbit/s, equivalent to that of uncompressed 8K ultrahigh definition video being streamed in real time,” said associate professor Masayuki Fujita, who led the team at Osaka University. “To make the entire system portable, we plan to integrate this multiplexer with resonant tunneling diodes to provide compact, multichannel terahertz transceivers.”

The team employed a fairly basic modulation scheme in which terahertz power was simply switched on and off to transmit binary data. More advanced techniques are available that can push even higher data rates toward 1 Tbit/s into a given bandwidth allocation.

“The new multiplexer can be mass-produced, just like computer chips, but much simpler. So large-scale market penetration is possible,” said professor Tadao Nagatsuma of Osaka University. “This would enable applications in 6G and beyond, as well as the Internet of Things, and low probability of intercept communications between compact aircraft such as autonomous drones.”

The research was published in Optica (www.doi.org/10.1364/optica.420715).