Terahertz band (0.1 to 10 THz) with high carrier frequency and large available bandwidth has become a promising candidate to meet the 100 Gbit/s or even 1 Tbit/s data rate required by the future six-generation (6G) mobile communication networks. Compared with the all-electrical methods to generate terahertz signals, the photon-assisted technology can break the bottleneck of the bandwidth limit of the electronics devices, and generate the terahertz signal with high frequency, large bandwidth, flexible tunability and easy integration with the large capacity fiber link. In this paper, we introduce the typical methods to generate terahertz signals based on the photon-assisted technology, and review the representative achievements in different areas of terahertz communication, such as the large capacity terahertz transmission, the long distance terahertz transmission, the real-time terahertz communication, and the integrated terahertz sensing and communication. Based on the photon-assisted technology and various key techniques, devices and advanced digital signal processing (DSP) algorithms, we have obtained many great achievements in broadband terahertz communication and sensing, and the experimental setups and results have also been demonstrated in detail.

From the perspective of wireless transmission distance in the terahertz-band (THz-band), the 10-100 m, 100-1000 m, and ≥1000 m ranges are recommended for indoor communications, medium-distance communications, and long-distance communications, respectively. However, most existing photonic terahertz communication demonstrations reported in previous studies have a distance of less than 100 m, with some being even shorter at 10 m or 1 m. In this study, by combining high-gain and high-sensitivity terahertz modules, as well as signal processing technology, we have successfully demonstrated transmission over 850 m with a net rate of 50 Gbit/s at a 320 GHz carrier frequency through outdoor field experimental verification. This particular demonstration represents the most significant distance-rate product, as well as the longest wireless distance achieved so far for photonic terahertz wireless communication. The results demonstrate that the integration of terahertz photonics, electronics, and cutting-edge DSP algorithms, has the potential to enable long-distance and high-speed wireless communication for frequencies ≥300 GHz. Our work represents another significant stride towards achieving our goal of realizing the world's first photonic terahertz-wave communication over kilometer-level distances.

The coexistence needs of sensing and communication in millimeter-wave (mmW) bands have urgently driven the seamless integration of sensing and communication in the upcoming mmW era. However, the time-frequency competition between the two functions makes it difficult to accommodate both high sensing resolution and large communication capacity. In this paper, we have designed a W-band fiber-wireless link with the integrated sensing and communication functions enabled by electromagnetic polarization multiplexing. The ultra-wideband fiber-wireless link in W band is enabled by the asymmetrical single-sideband modulation along with the optical heterodyne up-conversion. The electromagnetic polarization multiplexing allocates the sensing and communication functions on two orthogonal electromagnetic polarizations, respectively. Thus, all time-frequency resources of the fiber-wireless link can simultaneously serve these two functions without any resource competition, contributing to an ultra-high spatial resolution and an ultra-large data capacity at the same time. Our experimental results show the spatial resolution of up to 15 mm and data rate as high as 92 Gbit/s were simultaneously realized in W band after delivering over a 10.8-m wireless distance. The overall improvement of both the sensing and communication performance, to the best of our knowledge, led to a record capacity-resolution quotient of 61.333 Gbit/s/cm. In addition, we have qualitatively investigated the integrated sensing and communication fiber-wireless link, in terms of the carrier frequency, system bandwidth, multi-mmW access, and electromagnetic polarization crosstalk.

We experimentally demonstrate a large-capacity and long-haul photonics-aided dual-polarization (DP) terahertz wireless transmission system at 300 GHz. Orthogonal frequency division multiplexing (OFDM) scheme is employed to resist dispersion effects in the fiber link and multipath effects in the wireless link. To extend wireless transmission distance, we deploy high-gain dielectric plano-convex lenses, conical antennas (CAs), low-noise amplifiers (LNAs) as well as integrated mixer/amplifier/multiplier chain (IMAMC). We propose and utilize a low-complexity multiple-input and multiple-output (MIMO) hybrid time-frequency-polarization domain (TFPD) trigonometric-memory-polynomial (TMP) nonlinear equalizer (NLE), which is utilized to simultaneously eliminate in-phase/quadrature (I/Q) imbalance, inter-symbol interference (ISI), inter-carrier interference (ICI), polarization crosstalk and nonlinear impairments for DP-OFDM signals. Compared to the traditional MIMO Volterra-NLE, the MIMO-TFPD-TMP-NLE reduces the required number of real multiplications by 37.7%. By utilizing advanced THz modules and DSP algorithms, we have successfully achieved a record-breaking air interface user rate (AIUR)-distance product of 50.6 Gbit/s·km (253 Gbit/s × 0.2 km) in the THz band (above 0.3 THz).

As the mobile communication evolves from sub-6GHz to millimeter wave (MMW) frequency bands, the demand for high-speed wireless transmission rates exceeding hundreds of gigabits per second is becoming more and more prominent. It is one of the important cornerstones supporting numerous emerging bandwidth-consuming applications represented by the metaverse, digital twin and so on. So far, there is a huge room for improvement in wireless transmission rate, which is far inferior to the transmission capacity of fiber optic links. In this paper, we have proposed and experimentally demonstrated a large-capacity photonics-assisted MMW wireless communication system over 20-km fiber and 1.3-m wireless transmission at the W band. A dual-polarized single-input single-output (SISO) wireless link, instead of the commonly used 2×2 multiple-input multiple-output (MIMO) links, is used for the transparent transmission of optical polarization division multiplexing signal, which significantly simplifies the system complexity and enhances its robustness. In addition, the transmission performance is further improved by employing an advanced MIMO Volterra nonlinear equalizer. With the bit error ratio threshold of 2×10-2, a record single-lane single-carrier wireless air interface rate (WAIR/ch/λ) up to 504 Gb/s has been achieved for the first time. This solution we proposed provides opportunity for progress in the wireless air interface capacity close to the fiber-optic transmission capacity in the fiber-wireless integration transmission systems.

We demonstrate 6G-oriented 100 GbE real-time streaming service applications in fiber-THz-fiber seamless transmission with a record net data rate of 103.125 Gbps at 370 GHz enabled by photonic up-/down-conversion and digital coherent modules.