Conventional electronic technologies face fundamental limitations in generating stable high-frequency signals beyond 350 GHz, including reduced output power and increased phase noise. These challenges have hindered the realization of ultra-high-speed wireless communication in the terahertz regime, which is expected to play a key role in future 6G systems.
To overcome these challenges, the research team developed a microcomb-driven terahertz wireless communication system that combines fiber-coupled microcombs with high-order modulation techniques. The system leverages the high frequency stability and low phase noise of microcombs to generate a low-noise terahertz carrier. This enabled wireless transmission at 112 Gbps in the 560 GHz band, significantly exceeding conventional terahertz communication systems at these frequencies, typically limited to data rates of a few to several tens of gigabits per second, and demonstrating for the first time 100 Gbps-class wireless communication beyond 420 GHz, opening a new frontier in high-frequency wireless technologies.
The system is based on a compact and stable microcomb device using a fiber-coupled microresonator. By directly bonding an optical fiber to a silicon nitride microresonator, the researchers eliminated the need for precise optical alignment, enabling significant miniaturization and improved operational stability. This configuration also allowed high-power optical pumping and long-term stable operation, establishing a platform for low-noise terahertz signal generation. In addition, the integration of a temperature control function for the microresonator improves the reproducibility of optical resonance characteristics and enhances robustness against environmental temperature fluctuations.
In the wireless transmission experiment, two highly stable optical carriers were generated via optical injection locking of the microcomb and modulated using QPSK and 16QAM formats. These signals were converted into a 560 GHz terahertz wave through photomixing and transmitted wirelessly. At the receiver, the signals were recovered using heterodyne detection with a sub-harmonic mixer. As a result, data rates of 84 Gbps (QPSK) and 112 Gbps (16QAM) were achieved.
"This result represents a major step toward practical 6G wireless systems and ultra-high-speed mobile backhaul," said Prof. Takeshi Yasui of Tokushima University.
This work establishes a key technological foundation for ultra-high-speed mobile backhaul links and photonic–wireless integrated networks in 6G systems. Future work will focus on further reducing phase noise, enabling higher-order modulation formats, and extending transmission distance through improved terahertz output power and antenna design.
