112 Gbit/s single-wavelength FSO communication with 104.8 km horizontal atmospheric link over Qinghai Lake

The application of ultra-high-bandwidth free-space optical (FSO) communication has become a widely researched hotspot. In remote areas without network coverage, the low altitude platform (LAP), such as airships, drones, etc., can provide a low-cost and rapid deployment emergency FSO communication platform covering hundreds of kilometers and has immeasurable application prospects. In our work, we experimentally demonstrated a line rate of 112 Gbit/s FSO communication at a distance of 104.8 km over Qinghai Lake. By adopting the methods of polarization multiplexing (PM), high-order quadrature amplitude modulation (n-QAM), automatic gain optical amplification (AGOA), etc., we have achieved a long-haul and high-bandwidth laser communication in atmospheric link with the optimum bit error rate (BER) of 3E-3 (zero-BER after error-correction) for a time-length of 50 s. It is particularly emphasized that the AGOA effectively can suppress the fluctuation of received optical power caused by atmospheric turbulence scintillation effect in Qinghai Lake, which solved the difficulty of detection-demodulation with ultra-high-speed laser signals. In addition, the efficient soft decision forward error correction (SD-FEC) also improved the stability of the communication link, which played a crucial role in the success of this experiment. Our design of non-adaptive optical (AO) system is very suitable for application in small-scale LAP and will potentially become an important foundation of the large-capacity nonterrestrial network (NTN) based on LAP. To the best of our knowledge, this experiment verified the feasibility of single-wavelength (1556.15 nm) 112 Gbit/s high-bandwidth laser signal transmission with a long-haul of 104.8 km in low-altitude horizontal atmospheric link for the world's first time. To a large extent, our research findings also have great application value in the field of low-altitude economy.