Terahertz technology breakthrough promises faster data transfer

An innovative approach advances terahertz technology, facilitating faster data transmission and wider adoption.

Terahertz technology has the potential to address the growing need for faster data transfers, but converting terahertz signals to various lower frequencies remains a challenge. Recently, Japanese researchers have developed a new approach to convert terahertz signals into uplink and downlink signals in a waveguide. This is achieved by dynamically changing the waveguide’s conductivity using light, creating a time boundary. Their breakthrough could lead to advances in optoelectronics and improved telecommunications efficiency.

In the information age, the demand for faster data transmission is constantly growing, driven by rapid advances in fields such as deep learning and robotics. In this context, more and more scientists are exploring the potential of using terahertz waves to develop high-speed telecommunications technologies.

However, to use the terahertz band efficiently, we need frequency division multiplexing (FDM) techniques to transmit multiple signals simultaneously. Of course, being able to up-convert or down-convert the frequency of a terahertz signal to another arbitrary frequency is a logical prerequisite for FDM. This has unfortunately proven to be quite difficult with current technologies. The main problem is that terahertz waves are very high frequency waves from the perspective of conventional electronics and very low energy light in the context of optics, beyond the capabilities of most devices and configurations in both areas. Therefore, a radically different approach will be required to overcome current limitations.

Innovative solution for frequency conversion

Surprisingly, in a recent study published in Nanophotonics On May 20, 2024, a research team including Assistant Professor Keisuke Takano from the Faculty of Science at Shinshu University, Japan, presented an innovative solution for frequency conversion of terahertz waves. Their paper was co-authored by Fumiaki Miyamaru from Shinshu University, Toshihiro Nakanishi from Kyoto University, Yosuke Nakata from Osaka University, and Joel Pérez-Urquizo, Julien Madéo, and Keshav M. Dani from the Okinawa Institute of Science and Technology.

The proposed strategy is based on frequency conversions that occur in time-varying systems. Just as a waveguide confines a traveling wave packet in space, there is an analogous concept that occurs in time, known as temporal waveguiding. Simply put, variations that occur throughout a system over time will act as a “temporal boundary”. Just like spatial boundaries (e.g., the interface between two different media), temporal boundaries can change the dispersion properties of the waveguide, giving rise to different propagation modes at new frequencies.

Experimentation and potential applications

To create this time boundary, the researchers first layered a GaAs waveguide on a thin metal layer. As terahertz waves passed through the waveguide in transverse magnetic (TM) mode, they shone light onto the bare GaAs surface. The resulting photoexcitation of the top surface instantly changed its conductivity, transforming the lower metallized waveguide into a parallel doubly metallized waveguide. This transition from one waveguide structure to another acted as a time boundary, at which the incident TM modes of the bare waveguide coupled to the transverse electromagnetic (TEM) mode of the doubly metallized waveguide. Since the dispersion curve of the TEM mode occupies a lower frequency range than the incident TM mode, this approach produces a downward-shifted terahertz wave.

The research team conducted experiments that ultimately validated their in-depth theoretical analysis of the proposed frequency conversion method. Thus, the results of this study point to a promising future for terahertz technology in the future. Excited by the results, Dr. Takano said, “Frequency conversion devices for terahertz waves have the potential to be applied to future ultra-high-speed wireless communications. For example, they could enable information replication between terahertz wave frequency channels carrying different data. There could also be devices in which terahertz wave information processing circuits are integrated with various optical processing components.” It is worth noting that upconversion using the proposed approach was also demonstrated in “F. Miyamaru et al., Phys. Rev. Lett., 127, 053902 (2021). » Moreover, up- and down-conversion can be switched by manipulating the polarization of the input terahertz waves, which would help make FDM in the terahertz range more practical.

Furthermore, the current frequency conversion method is not strictly limited to terahertz waveguides and could also have important implications in the field of optics. “It is important to recognize that the concept of this study extends beyond the terahertz frequency range and can also be applied to the optical frequency range. Ultrafast frequency conversion devices comprising optically modulated waveguides with indium tin oxide could also be possible, based on recent findings,” notes Dr. Takano.

Further advances in this area could ultimately lead to faster and more energy-efficient telecommunications, helping us build a more interconnected and sustainable society.

Reference: “Downconversion of terahertz waves at optically induced time boundaries in GaAs waveguides” by Keisuke Takano, Satoko Uchiyama, Shintaro Nagase, Yuka Tsuchimoto, Toshihiro Nakanishi, Yosuke Nakata, Joel Pérez-Urquizo, Julien Madéo, Keshav M. Dani and Fumiaki Miyamaru, May 20, 2024, Nanophotonics.
DOI: 10.1515/nanoph-2024-0010

Funding: Japan Society for the Promotion of Science, JST PRESTO, Preliminary Research on Embryonic Science and Technology, Okinawa University of Science and Technology, Takano Gakujutsu-Shinko-Zaidan Foundation