Terahertz devices can significantly increase the speed of data transfer and processing. In this study, the researchers developed a new strategy to convert the frequency of terahertz waves traveling in a waveguide into another arbitrary frequency in the terahertz range, a conversion that is essential for practical applications. Credit: SciTechDaily.com
Innovative approaches are advancing terahertz technology, facilitating faster data transmission and wider adoption.
Terahertz technology has the potential to meet the growing need for faster data transfer rates, but converting terahertz signals to a range of lower frequencies remains a challenge. Recently, Japanese researchers have devised a new technique to upconvert and downconvert terahertz signals in a waveguide. This is achieved by using light to dynamically change the waveguide's conductivity and create a temporal boundary. This breakthrough could lead to advances in optoelectronics and improved communication efficiency.
As the information age advances, the demand for faster data transmission continues to grow due to rapid advances in fields such as deep learning and robotics. Against this backdrop, more and more scientists are exploring the possibility of using terahertz waves to develop high-speed communication technologies.
However, to use the terahertz band efficiently, frequency division multiplexing (FDM) techniques are needed to transmit multiple signals simultaneously. Of course, being able to upconvert or downconvert the frequency of a terahertz signal to another arbitrary frequency is a logical prerequisite for FDM. Unfortunately, this proves to be very difficult with current technology. The main problem is that terahertz waves are extremely high-frequency waves from the point of view of conventional electronics, and very low-energy light from the point of view of optics, beyond the capabilities of most devices and configurations in both fields. Thus, a fundamentally different approach is needed to overcome the current limitations.
Innovative Solutions for Frequency Conversion
Surprisingly, a recently published study Nanophotonics On May 20, 2024, a research team led by Assistant Professor Keisuke Takano of the Faculty of Science at Shinshu University reported an innovative solution for frequency downconversion of terahertz waves. The paper was co-authored by Fumiaki Miyamaru of Shinshu University, Toshihiro Nakanishi of Kyoto University, Yosuke Nakata of Osaka University, Joel Pérez Urquizo, Julian Madeo, and Keshav M. Dani of the Okinawa Institute of Science and Technology.
The proposed strategy is based on frequency transformations that occur in time-varying systems. Just as a waveguide confines traveling wave packets in space, a similar concept occurring in time is known as time guiding. Simply put, any changes that occur throughout the system over time act as a “time boundary”. Similar to a spatial boundary (e.g., an interface between two different media), a time boundary modifies the dispersion properties of the waveguide, giving rise to different propagation modes at new frequencies.
Experiments and potential applications
To create this temporal boundary, the researchers first placed a GaAs waveguide on top of a thin metal layer. As terahertz waves pass through the waveguide in transverse magnetic (TM) mode, light is shone on the exposed GaAs surface. As a result, the top surface is photoexcited and its conductivity changes instantaneously, essentially transforming the bottom-metallized waveguide into a parallel double-metallized waveguide. This transition from one waveguide structure to another acts as a temporal boundary where the incident TM mode of the exposed waveguide couples with the transverse electromagnetic (TEM) mode of the double-metallized waveguide. Given that the dispersion curve of the TEM mode occupies a lower frequency range than the incident TM mode, this approach generates terahertz waves that are shifted downward in frequency.
The research team conducted an experiment to finally verify the thorough theoretical analysis of the proposed frequency conversion method. The results of this study therefore paint a bright future for future terahertz technology. Excited by the results, Dr. Takano stated, “Terahertz wave frequency conversion devices may be applicable to future ultrafast wireless communications. For example, it would enable information duplication between terahertz wave frequency channels carrying different data. There may also be devices in which terahertz wave information processing circuits are integrated with various optical processing components.” Notably, upconversion via the proposed approach was reported in a paper by F. Miyamaru. others., Phys. Rev. Lett., 127, 053902 (2021)”. Moreover, up-conversion and down-conversion can be switched by manipulating the polarization of the input terahertz wave, making FDM in the terahertz region more convenient.
Furthermore, this frequency conversion method is not strictly limited to terahertz waveguides, but may also have important implications in optics: “It is important to realize that the concepts in this research can be applied beyond the terahertz frequency range, into the optical frequency range as well. Based on the results of our recent work, ultrafast frequency conversion devices with optically modulated waveguides using indium tin oxide may also be feasible,” said Dr. Takano.
Further developments in this field could ultimately lead to faster and more energy-efficient communications, contributing to building a more interconnected and sustainable society.
Reference: “Frequency downconversion of terahertz waves at optically induced time boundaries in GaAs waveguides,” Keisuke Takano, Satoko Uchiyama, Shintaro Nagase, Yuka Tsuchimoto, Toshihiro Nakanishi, Yosuke Nakata, Joel Pérez Urquizo, Julian Madeo, Keshav M. Dani, Fumiaki Miyamaru, May 20, 2024, Nanophotonics.
DOI: 10.1515/nanoph-2024-0010
Supported by: Japan Society for the Promotion of Science, Japan Science and Technology Agency (JST) PRESTO, Okinawa Institute of Science and Technology Graduate University, Takano Academic Foundation
