Feng Liu

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.

Quantum key distribution (QKD) has emerged as a promising technique for secure communication in the post-quantum era, offering information-theoretic security against eavesdroppers with unlimited computational power. While fiber-based and satellite QKD systems have demonstrated impressive distances and key rates, terrestrial free-space QKD, which shows potential for secure mobile and wireless payment applications, remains relatively under-investigated due to severe ambient light interference. Here, we present a QKD link operating in the ultraviolet-C (UV-C) region, which is, to the best of our knowledge, the first such example. This has the potential to leverage the “solar-blind” nature of the UV-C region and mitigate sunlight interference. By integrating high-speed AlGaN micro-LEDs with silicon photomultiplier (SiPM)-based single-photon detectors (SPDs), we achieve a secure key rate (SKR) exceeding 1 Mbit/s. Furthermore, we analyze the system’s robustness to ambient light and propose a strategy for full sunlight rejection. Our results establish UV-C as a promising spectral window for terrestrial free-space QKD, paving the way for QKD implementations in daylight conditions.

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.

Low photon flux optical wireless communication (OWC) links are difficult to operate under normal daylight conditions as the interference from daylight will overwhelm any signal. However, in the UV‐C region of the spectrum, light from the sun is highly attenuated, offering the possibility of link operation. In this paper, ultralow photon flux OWC links using a UV‐C micro‐LED and a silicon photomultiplier (SiPM) based UV‐C single‐photon detector (SPD) are reported. A 1 megabaud per second (MB s⁻¹) symbol rate 128‐pulse‐position modulation (128‐PPM) link is demonstrated with 7.7 transmitted photons per bit, corresponding to 0.97 detected photon per bit. A maximum bit rate of 120 Mbit s⁻¹ is achieved in 8‐PPM links with a transmitted power of 1.7 nW. In addition, a 500 MHz single‐photon link is established with a bit error rate (BER) of and a measured bit rate of 2.12 Mbit s⁻¹, showing the potential for a quantum key distribution (QKD) system operating at the UV‐C region.