Telecommunications
Information communication technologies, Smart devices

Development of compact diplexers based on a silicon chip
Division of Advanced Electronics and Optical Science, Graduate School of Engineering Science
Associate Professor Masayuki Fujita
Researchmap https://researchmap.jp/fujitamasayuki?lang=en

Telecommunications

Abstract
People around the world are increasingly using mobile devices
to access the internet and the number of connected devices ismultiplying exponentially. Soon machines will be communicatingwith each other in the Internet of Things which will require evenmore powerful wireless networks able to transfer large volumesof data fast. Terahertz waves are a portion of the electromagnetic
spectrum that has a raw spectral bandwidth that is far broader
than that of conventional wireless communications, which is based
upon microwaves. A new design of ultra-small silicon chip calleda multiplexer will effectively manage terahertz waves which are
key to the next generation of communications: 6G and beyond.
The developed terahertz multiplexers, which are economical tomanufacture, will be extremely useful for ultra-broadband wirelesscommunications. The multiplexer is made from pure silicon for terahertz-range communications in the 300-GHz band. To control thegreat spectral bandwidth of terahertz waves, a multiplexer, which isused to split and join signals, is critical for dividing the information
into manageable chunks that can be more easily processed andso can be transmitted faster from one device to another. The shapeof the chips is the key to combining and splitting channels so that
more data can be processed more rapidly.

Schematic of the integrated multiplexer, showing broadband terahertz wave being split into four different frequencies, where each is capable of carrying digitalinformation.

▍ Significance of the research and Future perspective
A typical four-channel optical multiplexer might span more than2000 wavelengths. This would be about two meters in length in the300-GHz band. Our device is merely 25 wavelengths across, which
offers dramatic size reduction by a factor of 6000. The developed
multiplexer covers a spectral bandwidth that is over 30 times thetotal spectrum that is allocated in Japan for 4G/LTE, the fastest mobile technology currently available and 5G which is the next generation, combined. As bandwidth is related to data rate, ultra-highspeed digital transmission is possible with the new multiplexer. Our
four-channel multiplexer can potentially support an aggregate data
rate of 48 Gbit/s, equivalent to that of uncompressed 8K ultrahighdefinition video being streamed in real-time. To make the entire
system portable, we will integrate this multiplexer with resonant
tunneling diodes to provide compact, multi-channel terahertz transceivers. The present modulation scheme was quite basic; terahertz
power was simply switched on and off to transmit binary data.
More advanced techniques are available that can squeeze evenhigher data rates towards 1 Terabit/s into a given bandwidth allocation. The developed multiplexer can be mass-produced, just likecomputer chips, but much simpler. So large-scale market penetration is possible. 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.

Photograph of the silicon multiplexer.

P a t e n t Japanese Patent Application No. 2020-128220
Headland, Daniel; Withayachumnankul, Withawat; Fujita, Masayuki et al. Gratingless integrated tunneling multiplexer for terahertz waves. Optica. 2021; 8
Tr e a t i s e(5): 621-629. doi: 10.1364/OPTICA.420715
UR
L https://www.jst.go.jp/pr/announce/20210429/index.html
K e y w o r d 6G, communications, multiplexer, silicon, terahertz