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.

We provided a feasible solution for 800-Gb/s per carrier long-distance wavelength division multiplexing (WDM) coherent optical fibre transmission based on offline DSP. We experimentally demonstrate 5-carrier 125-GHz-spacing WDM coherent optical fibre transmission achieving 2000-km transmission distance and 800-Gb/s net bit rate per carrier. We utilized 100-Gbaud truncated probabilistically shaped (TPS) polarization-multiplexed 64QAM format in this work. In terms of advanced components, the high-speed digital-to-analog converter with 35-GHz 3 dB-bandwidth and Raman-amplified ultra-large-area fibre were utilized to achieve higher baud-rate and longer transmission distance. In terms of modulation format, we changed PS to TPS to obtain a more suitable shaping depth, and make the shaped signal better suited to the DSP process of coherent optical communication, including constant modulus algorithm (CMA) equalizer. Besides, our results show that the TPS-64QAM signal with 5-bit/symbol/polarization entropy outperforms the standard-32QAM with a same bit rate by around 1 dB sensitivity gain. Furthermore, we proposed a multiple-input multiple-output (MIMO) Volterra equalizer (VE), which consists of a 1 ^st -order 2 × 2 MIMO complex-valued widely linear (WL) equalizer and a 2 ^nd -order real-valued nonlinear equalizer. Our proposed MIMO VE can effectively resolve the impact of In-phase/quadrature (IQ) imbalance and IQ skew, and compensate linear and nonlinear impairments at the same time. We also utilized partial kernel VE to reduce the complexity by retaining part of the 2 ^nd -order kernels.

In this letter, a novel physical layer encryption method based on digital chaos is proposed for the security in high-speed intensity modulation and direct detection (IM/DD) discrete multi-tone (DMT) transmission system. In the proposed encryption scheme, a random interleaving method is used, which further enhances the ability to encrypt the quadrature amplitude modulation (QAM) constellation and improves the transmission performance. In addition, probabilistic shaping (PS) technique is also cascaded into the encrypted transmission system for the first time. Adopting the proposed algorithm, we experimentally demonstrated the transmission of 100-Gbit/s encrypted 64QAM and PS-64QAM DMT signals over 2-km standard single-mode fiber (SSMF).

We proposed and established a large-capacity, long-distance wireless millimeter-wave (mm-wave) signal delivery system at W-band based on photonics-aided mm-wave generation technology, polarization-division-multiplexing (PDM), and advanced devices. We demonstrated the wireless transmission of 10-Gbaud PDM-QPSK, PDM-16QAM, and PDM-PS-64QAM mm-wave signals in the W-band up to 4.6-km, respectively. The multiple-input multiple-output (MIMO) Volterra equalizer (VE) is employed during the Rx offline digital signal processing (DSP) to compensate for impairments and further improve the system transmission performance. Our demonstrated system can generate and deliver 10-Gbaud (110 Gb/s) PDM-PS-64QAM (5.5 bits/symbol/polarization) mm-wave signal at 88.5-GHz over 4.6-km wireless distance with a bit-error-rate (BER) below the soft-decision forward error correction (SD-FEC) threshold of 2.4 × 10 ⁻² . Considering the SD-FEC threshold of 2.4×10 ⁻² with 20% overhead, the maximum net rate of 91.6 Gb/s in this system can be achieved. To the best of the authors’ knowledge, it's the first time to demonstrate single-carrier PDM-PS-64QAM (91.6 Gb/s) wireless mm-wave signal delivery over 4.6 km at W-band.

We experimentally demonstrated a 10-channel 50-GHz-grid wavelength division multiplexing (WDM) signal transmission over 400-km standard single-mode fiber (SSMF) with the net bit rate of 614.4 Gbps/carrier and the spectral efficiency (SE) of 12.288 b/s/Hz, which is the highest SE for 256QAM to the best of our knowledge. Thanks to the joint pre-equalization and Volterra nonlinear equalization (VNLE), 49-Gbaud polarization division multiplexing (PDM) 256-ary quadrature amplitude modulation (256QAM) signal transmission with a novel constellation using probabilistic shaping (PS) and geometric shaping (GS) techniques is realized, considering the 0.828-normalized generalized mutual information (NGMI) low-density parity-check (LDPC) threshold with 25% overhead. Compared with the regular 256QAM at the same net bit rate, the designed hybrid PS/GS 256QAM at the expense of 1-Gbaud increase in the symbol rate obtains 1.7-dB and 1.5-dB shaping gain in single-channel case and WDM case, respectively. Meanwhile, an improvement of at least 0.6-dB in optical signal to noise ratio (OSNR) over the hybrid PS/GS 256QAM is achieved in comparison with PS-256QAM for both single-channel and WDM transmission.

Indoor Optical Wireless Communication (OWC) provides a promising solution for high-capacity, low-latency, and electromagnetic interference-resistant wireless communication. Over the past decade, there has been extensive research addressing key challenges in indoor OWC. This article provides an overview of the current development status, key technologies, and challenges faced in the field of indoor OWC. Furthermore, at the end of this overview, an experimental demonstration of an indoor non-line-of-sight (NLOS) OWC system utilizing a spatial light modulator (SLM) for beam steering is demonstrated, which is expected to inspire research on related technologies.