Telecommunications
Information communication technology, Smart device, Sensing

Terahertz silicon photonics for 6G andbeyond information communication systems
Division of Advanced Electronics and Optical Science, Graduate School of Engineering Science
Associate Professor Masayuki Fujita
https://researchmap.jp/fujitamasayuki?lang=en

Telecommunications

Abstract
A wide untapped bandwidth exists between radio and lightwaves in the electromagnetic spectrum known as terahertz waves.
Terahertz frequencies (0.1–10 THz) combine the penetration ofradio waves and large bandwidth of light, making them excellentcandidates for next-generation 6G information communication
technology and beyond, such as ultra-broadband wireless communication, spectroscopic sensing, nondestructive imaging, andhigh-resolution ranging. However, terahertz frequencies are at theupper limit of the capabilities of conventional electronics, and thedevelopment of terahertz devices and systems is a challenging
field that requires interdisciplinary research. In this study, we have
explored terahertz silicon photonics, which employs silicon semiconductors as a low-loss dielectric medium for terahertz-wave manipulation, to overcome the information loss in the terahertz band.
We have developed ultralow-loss waveguides in the 1-THz band
and an efficient interface integrated with active terahertz devices in
the 0.3-THz band.

▍ Significance of the research and Future perspective
Terahertz silicon photonics can facilitate the development ofadvanced communication and sensing systems. Terahertz communications could realize extremely low-latency wireless communications for advanced remote-control applications such as automateddriving, autonomous operation, drones, and robots, which canbe remotely controlled by artificial intelligence systems. Terahertz
waves could enhance the precision and resolution of sensing owing to their shorter wavelength compared with microwaves for 6G
and beyond communication generations.

▍ Background & Results
Globally, the use of mobile devices for accessing the internet
and the number of connected devices is increasing exponentially.
Soon, machines will communicate with each other over the Internetof Things, which will require even more powerful wireless networks
capable of transferring large volumes of data rapidly. Terahertz
waves are a section of the electromagnetic spectrum that have araw spectral bandwidth far broader than that of conventional microwave-based wireless communications. A study on terahertz silicon
photonics to effectively manage terahertz waves is critical for thedevelopment of subsequent 6G and beyond generations of information communication systems. Additionally, a low-loss platform
for integrating terahertz devices is essential for various practicalapplications. However, the propagation loss of transmission lines
in conventional electronics is high in the terahertz region, owing
to high ohmic loss in metals. Hence, an alternative metal-free integrated platform is necessary for manipulating terahertz waves.
Photonic crystals are metal-free dielectric microstructures with periodic refractive index distributions on scales comparable to wavelengths of interest. Various advanced terahertz devices based on
silicon photonic crystals and related microstructures have been developed, including ultralow-loss waveguides, compact frequency
selectors, compact and broadband antennas, and high-Q cavities.
Active functions, including terahertz-signal generation, detection,
frequency conversion, and modulation, can be subsequently integrated with the terahertz silicon photonics platform. Accordingly,
an efficient mode converter suitable for the deep-subwavelength
region was developed in this study for integrating terahertz activedevices.

Developed terahertz circuit based on terahertz silicon photonics

Fabricated one-terahertz band silicon waveguideP a t e n t Japanese Patent Application No. 2020-128220
Yu, Xiongbin; Headland, Daniel; Nishida, Yosuke et al. Hybrid integration between resonant tunneling diodes and unclad microphotonic diplexer for dualchannel coherent terahertz receiver. IEEE Journal of Selected Topics in Quantum Electronics. 2022, 28 (3), 8500210, doi: 10.1109/JSTQE.2021.3130813
Tr e a t i s e
Koala, Ratmalgre; Maru, Ryoma; Iyoda, Kei et al. Ultra-low-loss and broadband all-silicon dielectric waveguides for WR-1 Band (0.75–1.1 THz) modules.
Photonics. 2022, 9 (8), 515, doi: 10.3390/photonics9080515
UR
L https://resou.osaka-u.ac.jp/ja/research/2021/20210429_2
K e y w o r d 6G, communications, terahertz, silicon, photonics