Case study: Photonics-Enabled Sub-THz Networks for Future C-RAN-Based 6G Infrastructure

Future 6G mobile networks will need to support dramatic growth in data traffic and User density. A key technological pathway to achieve this involves integrating fibre-optic infrastructure with ultra-high-frequency wireless links in the sub-terahertz (sub-THz) spectrum. By leveraging advanced photonic technologies, including high-speed photodiodes for optical-to-THz conversion, data-bearing optical signals can be transported through existing fibre networks and delivered directly to distributed access nodes. These access nodes, known as Remote Radio Heads (RRHs), then generate sub-THz wireless signals to provide Users with extremely high-capacity connections.

Fig. 1 Concept of future radio access network deploying optical signal distribution for sub-terahertz signal generation at remote radio head (RRH) to provide high-capacity network access.

In this experiment, this emerging sub-THz C-RAN architecture was validated using NDFF. An optical frequency comb with line spacing of 16.5 GHz was transmitted over 38 km of installed fibre between UCL and Telehouse, then used to generate signals to act as local oscillators for photonically pumped diode mixers. After transmission over NDFF, pairs of comb lines were filtered and photomixed on high-speed photodiodes (UTC-PDs). The resulting low phase-noise signals were used to pump sub-harmonic mixers for both up- and down-conversion of sub-THz wireless signals at the RRH. This process generated stable terahertz carriers suitable for both uplink and downlink transmission, effectively bridging fibre infrastructure with next-generation wireless access.

Using this configuration, a 165-GHz sub-THz wireless link capable of delivering data rates up to 100 Gbit/s within forward-error-correction (FEC) limits was demonstrated. A small reduction in performance was observed after transmission over the installed NDFF fibre, but these results confirm that photonics-enabled distribution and generation of sub-THz signals is a promising candidate technology for ultra-dense 6G deployments and for supporting the high-capacity demands expected in future urban networks.

Using the NDFF testbed has been essential in validating the feasibility and scalability of this architecture, directly contributing to the HASC Hub’s vision of deeply integrated fibre-wireless connectivity for next-generation networks.

For further information: contact Martyn Fice, ndff@ee.ucl.ac.uk

Published: 15 Feb 2026