Martyn John Fice

Terahertz (THz) wireless communication has emerged as a promising technology for future beyond-6G networks due to its abundant bandwidth resources. However, most experimental THz demonstrations to date are limited to single-band and point-to-point links, which limit their applications in practical multi-user wireless networks. In this work, we demonstrate the first photonically generated simultaneous multi-band THz communication system employing a single transmitter and two independent receivers. A custom-designed uni-travelling-carrier photodiode (UTC-PD)-integrated slot antenna is used as a broadband THz transmitter, enabling the simultaneous generation of THz signals in two industry-standard rectangular waveguide bands: the WR-5.1 band at 144 GHz for separate-reception links and 155 GHz for simultaneous-reception links, and the WR-3.4 band at 222 GHz. Independent photonically pumped WR-5.1 and electronically pumped WR-3.4 receivers are used to receive their respective band signals, either separately or simultaneously. For separate-receiving links, maximum data rates of 80 Gbit/s and 15 Gbit/s are achieved in the WR-5.1 and WR-3.4 bands, respectively. Under simultaneous transmission and reception, adjustment of the THz carrier frequency and transmitted THz power is further investigated. This enables balanced multi-band performance, achieving a data rate of 10 Gbit/s in both bands, and demonstrates the inherent flexibility and adaptability of photonically generated THz systems. These results highlight the potential of photonic THz technology for future multi-band, multi-user wireless access networks.

Terahertz communication is expected to be a key technology for future wireless networks, offering ultra-high capacity, beyond the limits of conventional radio-frequency systems. To enable practical implementation, investigating non-line-of-sight terahertz links is essential, but this remains largely unexplored. This paper presents an experimental demonstration of a non-line-of-sight terahertz link at 146.8 GHz using common building materials. The reflection and transmission properties of metal, glass, wood, plasterboard, and ceiling tile are characterised and fitted using Fresnel equations. Based on these measurements, reflection- and transmission-based links over a 1 m non-line-of-sight path are established, achieving maximum data rates of 40 Gbit/s and 50 Gbit/s, respectively, while satisfying the soft-decision forward error correction threshold. To the best of our knowledge, these results represent the highest reported data rates for non-line-of-sight terahertz links using building materials other than metal, showing the feasibility of high-speed indoor non-line-of-sight terahertz communications and providing guidance for future terahertz network implementation.

We demonstrate broadband wireless transmission at 2.54 Terahertz (THz) using directly modulated THz Quantum Cascade Laser (QCL) and Direct Current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). Fixed quadrature-amplitude modulation (QAM) transmission was investigated for modulation bandwidths of 2, 3, 4, 5 and 10 GHz, achieving gross data rates from 17.99 to 39.98 Gbit/s with modulation formats ranging from 16-QAM to 512-QAM. The measurements reveal a trade-off between modulation bandwidth, modulation order and bit-error rate arising from the limited usable bandwidth of the THz transmitter. Adaptive bit and power loading was subsequently implemented using measured subcarrier channel information, yielding gross data rates of 44.0 Gbit/s and 54.3 Gbit/s at the Hard-Decision Forward Error Correction (HD-FEC) and Soft-Decision Forward Error Correction (SD-FEC) thresholds, respectively. These results establish adaptive OFDM as an effective approach for efficiently utilizing the available bandwidth and increasing the throughput of THz wireless communication systems. To the best of the authors' knowledge, this represents the highest reported wireless transmission data rate at carrier frequencies above 1 THz.

Terahertz-frequency (THz) carrier waves in free-space optical (FSO) communications offer the potential for > 1 Tbit/s data rates and stable latency. They offer wider bandwidths than available in the microwave region, together with reduced scattering and relaxed pointing requirements compared with visible and near-infrared regions. However, 1–10 THz FSO communications systems have thus far been limited to data rates several orders of magnitude lower than those of infrared systems. This work describes an experimental demonstration of multi-gigabit-per-second FSO communication using a THz quantum cascade laser (QCL), opening a new frontier for next-generation wireless communications. The FSO communication system consists of a 2.4 THz QCL source as the transmitter and a room-temperature Schottky barrier diode detector as the receiver. By directly modulating the terahertz QCL, we achieved non-return-to-zero on-off keying (NRZ-OOK) with a transmission rate of up to 4 Gbit/s. We evaluated the performance of the communication link by analyzing the bit error rate (BER) of the demodulated signal at the receiver while examining its relation to received optical power, QCL modulation power, and various bias points. Our work establishes the foundation for high-speed optical wireless communication based on terahertz QCL technology systems.

Terahertz (THz) wireless technology, leveraging highly directional antennas, is a promising solution for future cellular networks. However, its susceptibility to micromobility-induced misalignment poses a significant challenge. This study presents a novel experimental framework for tracking user equipment (UE) motion across all six degrees of freedom (DOF) using laser-based video analysis. Micromobility characteristics are examined across various use cases, including holding, typing, reading, watching, and gaming, analysing motion distributions, axis correlations, and directional dependencies. A non-parametric 3D Markov Chain Monte Carlo (MCMC) model is developed, demonstrating the ability to replicate outage patterns when using multiple iterations. A link budget analysis of a photonically enabled THz system reveals substantial performance degradation due to micromobility, even in static holding scenarios. While increasing antenna coverage and implementing beamforming reduces misalignment effects, they do not eliminate outages, highlighting the need for further investigations of strategies to combat the effects of micromobility.

An Optical Injection Phase-Lock Loop coherent receiver has been tested against various levels of deep atmospheric fading to experimentally evaluate its feasibility in a ground-to-satellite optical communications application.

A photonic wireless bridge operating at a carrier frequency of 250 GHz is proposed and demonstrated. To mitigate the phase noise of the free-running lasers present in such a link, the tone-assisted carrier recovery is used. Compared to the blind phase noise compensation (PNC) algorithm, this technique exhibited penalties of 0.15 dB and 0.46 dB when used with aggregated Lorentzian linewidths of 28 kHz and 359 kHz, respectively, and 20 GBd 16-quadrature amplitude modulation (QAM) signals. The wireless bridge is also demonstrated in a wavelength division multiplexing (WDM) scenario, where 5 optical channels are generated and sent to the Tx remote antenna unit (RAU). In this configuration, the full band from 224 GHz to 294 GHz is used. Finally, a 50 Gbit/s transmission is achieved with the proposed wireless bridge in single channel configuration. The wireless transmission distance is limited to 10 cm due to the low power emitted by the uni-travelling carrier photodiode used in the experiments. However, link budget calculations based on state-of-the-art THz technology show that distances >1000 m can be achieved with this approach.

A photonic wireless bridge operating at a carrier frequency of 250 GHz is proposed and demonstrated. To mitigate the phase noise of the free-running lasers present in such a link, the tone-assisted carrier recovery is used. Compared to the blind phase noise compensation (PNC) algorithm, this technique exhibited penalties of 0.15 and 0.46 dB when used with aggregated Lorentzian linewidths of 28 and 359 kHz, respectively, and 20 GBd 16-quadrature amplitude modulation (QAM) signals. The wireless bridge is also demonstrated in a wavelength division multiplexing (WDM) scenario, where five optical channels are generated and sent to the Tx remote antenna unit (RAU). In this configuration, the full band from 224 to 294 GHz is used. Finally, a 50 Gbit/s transmission is achieved with the proposed wireless bridge in single channel configuration. The wireless transmission distance is limited to 10 cm due to the low power emitted by the uni-travelling carrier photodiode used in the experiments. However, link budget calculations based on state-of-the-art THz technology show that distances >1000 m can be achieved with this approach.

In this paper we propose multicore fiber (MCF) as the medium to transport the different signals associated with various wireless applications (ranging from access to fronthauling and backhauling) from the baseband unit (BBU) to the cell-site. Using 1 km of a 7-core MCF, we simultaneously transmit fronthaul and backhaul signals from the BBU to the cell site, where they are converted to carrier frequencies in the mm-wave and sub-THz band, respectively. The backhaul is evaluated with a 12.5 GBd 16-quadrature amplitude modulation (QAM) signal, whereas the fronthaul is evaluated with a 7 Gbit/s on-off keying (OOK) signal carrying 14 LTE-compatible channels. The fronthaul signal is generated with a novel compression technique that achieves an efficiency 3-times higher than the one obtained with the common public radio interface (CPRI) protocol. Optical heterodyining is implemented at the cell site for optical-to-RF conversion. The local oscillator (LO) signal required for optical heterodyning is transmitted in a dedicated core, reducing the system complexity and enabling its straight-forward reuse for uplink (UL) transmission. The experimental demonstration includes the simultaneous full-duplex transmission of both the fronthaul and backhaul signals, using 6 cores of the MCF at the same time and achieving a gross data rate of 57 Gbit/s.

The use of single sideband (SSB) signals and envelope detection is a promising approach to enable the use of economic free-running lasers in photonic THz communications. To combat the signal-signal beat interference (SSBI) associated with envelope detection, broad guard bands (GBs) may be used given the large unregulated spectrum available at THz frequencies (100 GHz - 10 THz). In this scenario, the conventional way of generating SSB signals through a digital SSB filter (here referred to as the CSSB scheme) would require quite high analog digital-to-analog converter (DAC) bandwidths. Digital virtual SSB (DVSSB) and analog virtual SSB (AVSSB) have been proposed in direct-detection optical systems for relaxing the DAC bandwidth requirements. In this paper, we compare the three techniques through simulations and implement them, for the first time, in a THz-over-fiber (ToF) system operating at 250 GHz. For the transmission experiments we employ 5 GBd 16-QAM signals with three different GBs (5.5 GHz, 4.75 GHz and 3.5 GHz). The simulations show that the best performance is obtained with the AVSSB technique, while the worst is obtained with the DVSSB scheme, where the quality of the generated sideband degrades with carrier-to-sideband power ratio. In the experimental transmissions, where receiver noise was the main source of noise, similar behavior was found between the three techniques. At the 3.5 GHz GB, however, the DVSSB exhibited a penalty of 1 dB with respect to the other two. This is likely to be due to nonlinear distortions caused by the increase in the virtual tone power.