Advancing High-Capacity Communication: Low-Loss and High-Data-Rate Terahertz Fiber Link

Significance 

The rapid proliferation of data-intensive technologies, such as Web3, applied artificial intelligence, and immersive realities, has created a demand for higher data rates and uninterrupted transmissions. However, the current fifth-generation wireless communication technology faces challenges in meeting these requirements due to bandwidth limitations. To overcome these limitations, researchers have explored multilevel multiplexing techniques. However, these solutions pose practical challenges. In this context, terahertz (THz) and sub-THz-band frequencies have emerged as a promising solution for future communication networks.

The THz frequency range, spanning from 100 GHz to 10 THz, remains largely unexplored but holds great potential for high-data-rate communication without the need for spectral enhancement methods. The use of higher frequencies in the THz range aligns with the Shannon theorem, which suggests that higher frequencies generally result in greater channel bandwidth and capacity. The THz frequency range has already proven useful in diverse applications, including enhanced imaging, range finding, and wireless communications.

In a new study published in the peer-reviewed Journal Optics Express presents a low-loss and high-data-rate THz fiber link using an efficient dielectric-waveguide interface. The study conducted by Dr. Ratmalgre Koala, Kei Iyoda, Dr. Weijie Gao, Prof. Masayuki Fujita, Prof. Tadao Nagatsuma from Osaka University and Prof. Yuji Matsuura from Tohoku University focused on developing a THz fiber link with low loss and high data rates. The researchers employed a silica glass tube with an inner silver coating and a hollow core as the fiber structure. Modal analysis was conducted, assuming a circular waveguide with a hollow circular cross-section, to ensure a broad transmission bandwidth and minimize signal distortion. The results showed that a 1-mm core fiber exhibited a larger dispersion bandwidth compared to a 0.7-mm core fiber, making it more suitable for high-capacity communication applications.

In addition to the fiber investigation, the authors also focused on developing a silicon waveguide interface for use in the THz fiber link. The selection of an unclad silicon waveguide was based on its low loss and broad bandwidth characteristics. To achieve a refractive index between silicon and air, the design incorporated an electromagnetic section and an array of through-holes. Impedance matching between the silicon taper and the fiber was crucial, and a tapered structure was implemented to enhance coupling efficiency. The waveguide coupler interface design ensured a good modal match between the fiber and silicon waveguide.

The research team conducted experiments to evaluate the loss and performance of fiber optic cables with different lengths and core diameters for high-data-rate communication. The results demonstrated that the 1-mm core fiber outperformed the 0.7-mm core fiber, exhibiting better transmittance and lower losses, particularly as the fiber length increased. Through transmission power measurements, propagation and coupling losses were estimated, showing that the 1-mm core fiber had lower losses compared to the 0.7-mm core fiber.

Furthermore, communication experiments revealed that the 1-mm core fiber achieved error-free data transmission at rates up to 22 Gbit/s, while the 0.7-mm core fiber achieved a maximum error-free rate of 14 Gbit/s due to dispersion phenomena. The successful transmission of high-definition video over a 1 m-long fiber highlighted the practicality and versatility of the THz fiber for various applications.

In conclusion, the researchers successfully developed a low-loss and high-data-rate terahertz fiber link using an efficient dielectric-waveguide interface. The use of a 1-mm core fiber demonstrated superior transmittance, lower losses, and achieved error-free data transmission at rates up to 22 Gbit/s. These findings hold promise for high-capacity communication applications in the future, addressing the limitations posed by current wireless communication technologies. The advancement of THz frequencies and the successful implementation of the fiber link contribute to the progress of data-intensive technologies, opening up new possibilities for Web3, applied artificial intelligence, immersive realities, and other emerging fields.

Advancing High-Capacity Communication: Low-Loss and High-Data-Rate Terahertz Fiber Link - Advances in Engineering

About the author

Masayuki Fujita received the Ph.D. degree from Yokohama National University, Yokohama, Japan, in 2002. Subsequently, he joined the Department of Electronic Science and Engineering, Kyoto University, Japan, and initiated research on photonic crystals. In 2011, he joined Osaka University, Japan, and was appointed the Research Director of the Strategic Basic Research Program CREST, “Development of terahertz integrated technology platform through fusion of resonant tunneling diodes and photonic crystals” from 2015 to 2021 and has been the Research Director of CREST “Development of integrated devices and systems to control time domain and space distribution of terahertz waves,” since 2021 of the Japan Science and Technology Agency. He is currently an Associate Professor with the Graduate School of Engineering Science, Osaka University. His research interests include terahertz electronic and photonic materials, and devices, and photonic nanostructures and microstructures, and their application systems. Dr. Fujita is a Fellow of the Optica.

About the author

Dr. Ratmalgre Koala is a published researcher with extensive experience in device and component design for operation in the microwave, the millimeter wave, and the terahertz regions. Dr. Koala received his M. E. in electrical engineering from Chungbuk National University, South Korea in 2016, and a Ph. D. in engineering from Graduate School of Engineering Science, Osaka University, Japan, in 2023. His Ph. D. research focused on high-resistivity crystalline silicon dielectric waveguides and their applications in the terahertz region. Dr. Koala Is currently a member of the millimeter wave group of RAL Space, a division of the UK’s science and technology facility council (STFC) that support research for earth observation.

About the author

Kei Iyoda received the B.E and M.E degrees in engineering science from Osaka University, Japan, in 2021 and 2023, respectively. Since 2023, he has been with Fiber Optic Devices Department, NEC Corporation, Japan. His research interests include topological photonics and photonic crystals, especially valley photonic crystals. Mr. Iyoda was the recipient of the Young Researcher Award of Technical Committee on Microwave Photonics and Terahertz Photonic-Electronics Technologies in Institute of Electronics, Information and Communication Engineers, Japan in 2023.

About the author

Weijie Gao received the M. Eng. Sci. degree in Telecommunications from University of New South Wales, Australia in 2016 and Ph.D. degree in Electrical and Electronic Engineering from The University of Adelaide, Australia in 2022. Since the same year, he has been working as a Postdoctoral Researcher in Graduate School Of Engineering Science at Osaka University, Japan. From 2016 to 2018, he was a visiting researcher with the Adelaide Applied Electromagnetics Group, The University of Adelaide. From 2018 to 2021, he was a founding member of Terahertz Engineering Laboratory, The University of Adelaide. Dr. Gao was the recipient of the Student Prize in the Asia-Pacific Microwave Conference, 2021 (APMC 2021). His doctoral thesis was awarded a Dean’s Commendation for Doctoral Thesis Excellence and The Gertrude Rohan Memorial Prize (Best PhD thesis in information and communications area) in 2022 by The University of Adelaide. In 2022, he was granted the Young Researcher Award by Osaka University in recognition of his contributions in beyond-5G communications. In 2023, he was awarded the University Doctoral Research Medal by The University of Adelaide in recognition of his Ph.D. research contributions in terahertz integrated platforms. His current research is mainly focused on photonics-inspired terahertz integrated components and communications systems towards 6G communications.

About the author

Yuji Matsuura received the Ph.D. degree in electrical communication engineering from Tohoku University, Japan, in 1992. He was a Research Engineer with Sumitomo Electric, Yokohama, Japan. From 1994 and 1996, he was a Postdoctoral Researcher with Rutgers University, New Brunswick, NJ, USA, and he became an Associate Professor with Tohoku University, Sendai, Japan. Since 2008, he has been a Professor with the Graduate School of Biomedical Engineering, Tohoku University. His research interests include application of specialty fiber optics in medical fields, hollow waveguides for ultraviolet and infrared light, and optics for soft and hard X-rays. His work has focused on development of healthcare systems based on spectroscopic analysis of body surfaces and exhaled breath using mid-infrared and ultraviolet light.

About the author

Tadao Nagatsuma received the Ph.D. degree in electronic engineering from Kyushu University, Japan, in 1986. From 1986 to 2007, he was with Nippon Telegraph and Telephone Corporation (NTT), Japan. Since 2007, he was with Osaka University, Japan, where he is a Professor with the Graduate School of Engineering Science. His research interests include millimeter-wave and terahertz photonics and their applications to wireless communications, sensing, and measurement. Dr. Nagatsuma is a Fellow of the Institute of Electrical and Electronics Engineers (IEEE), the Institute of Electronics, Information and Communication Engineers (IEICE), Japan, and the Electromagnetics Academy.

Reference

Ratmalgre Koala, Kei Iyoda, Weijie Gao, Yuji Matsuura, Masayuki Fujita, Tadao Nagatsuma. Terahertz fiber link using dielectric silicon waveguide interface.  Optics Express, Volume 31, Issue 5,  2023, Pages 7351-7362.

Go To Optics Express

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