Photonics-based ultra-stable tuneable THz system for 6G

The ultra-stable, tuneable THz system, developed within the 6G-ADLANTIK project, is based on frequency comb technology and enables carrier frequencies well beyond 500 GHz.

On the path to 6G, it is important to create terahertz (THz) transmission sources that offer high signal quality, and that cover as wide a frequency range as possible. Combining optical technologies with electronics is one possible way to achieve this in the future.

The 6G-ADLANTIK project focuses on developing components for the THz frequency range based on photonic and electronic integration.

Such THz components, yet to be developed, can then be used for innovative measurements and faster data transfers. These components will find applications not only in 6G communications but also in sensing and imaging.

Funded by the Federal Ministry of Education and Research of Germany (BMBF) and coordinated by Rohde & Schwarz, 6G-ADLANTIK has brought together the partners TOPTICA Photonics, Fraunhofer-Institut HHI, Microwave Photonics, Technical University Berlin, and Spinner. 

The proof-of-concept shows an ultra-stable, tuneable THz system for 6G wireless data transmission based on a photonic THz mixer which enables the generation of THz signals based on frequency comb technology.

In this approach, a photodiode efficiently converts an optical beat signal derived from lasers with slightly different optical frequencies into an electrical signal through a photomixing process. The antenna structure surrounding the photomixer translates the oscillating photocurrent into a THz wave.

The resulting signals can be modulated and demodulated for 6G wireless communications and can be tuned easily over a wide frequency range. The presented system can be extended for component characterization with coherently received THz signals.

A THz waveguide architecture simulation and design, as well as the development of ultra-low phase noise photonic reference oscillators, are also part of the scope of work for this project.

The ultra-low phase noise of the system is enabled by a comb-locked optical frequency synthesizer (OFS) in the TOPTICA laser engine. High-end instruments from Rohde & Schwarz are part of the setup. The R&S SFI100A wideband IF vector signal generator creates the baseband signals for the optical modulator with a sample rate of 16 GS/s. The R&S SMA100B RF and microwave signal generator generates a stable reference clock signal for the TOPTICA OFS system.

The R&S RTP oscilloscope samples the baseband signal after the photoconductive continuous wave (cw) THz receiver (Rx) at a sample rate of 40 GS/s for further processing and demodulation of the 300 GHz carrier frequency signal.

6G will enable new application scenarios in industry, medical technology and everyday life. Applications like the metaverse and extended reality (XR) will bring about new requirements for latency and data transmission rates that are not met by current communications systems. Although the ITU World Radio Conference 2023 (WRC23) identified for further study new frequency bands in the FR3 spectrum (7.125 - 24 GHz) for the first commercial 6G networks to be launched in 2030, the sub-THz frequency band up to 300 GHz will eventually be indispensable to realize the full potential of virtual reality (VR), augmented reality (AR), and mixed reality (MR) applications.