Miniaturised FSO system enables high-speed wireless comms

In a world that relies on high-speed internet and seamless communication, the absence of a reliable fibre connection can be a significant hurdle. Fortunately, a cutting-edge technology known as free-space optical communication (FSO) offers a fast, secure and licence-free solution for field-deployable wireless communication in areas where fibre connections are unavailable. Researchers from Nanjing University (NJU) have now developed a miniaturised FSO system that could potentially revolutionise high-speed wireless communication.

FSO has received increasing attention as an alternative to fibre communication for high-bandwidth wireless data transmission, in part due to its versatility across various scales of operation. It plays a crucial role in establishing high-speed satellite internet projects like Starlink, enabling global network coverage. It can also be used at the ground level, particularly in low-altitude scenarios, where its high-data-rate, licence-free and high-security connection makes it suitable for applications such as last-mile connections, disaster recovery efforts and military communications.

“In these flexible communication scenarios,” the NJU researchers wrote in the journal Advanced Photonics Nexus, “a portable and plug-and-play FSO system is essential.”

The NJU researchers developed a miniaturised FSO system which has now achieved an impressive communication bandwidth of 9.16 GBps over a 1 km link. This was accomplished using readily available commercial fibre optical communication transceiver modules, with no need for optical amplification.

The core of the miniaturised FSO system comprises a pair of FSO devices. Each FSO device is compact, measuring just 45 x 40 x 35 cm, with a weight of 9.5 kg and a power consumption of approximately 10 W. Each houses an optical transceiver module, an acquisition, pointing and tracking (APT) device, and its control electronics, all safely sealed within a box for rugged outdoor operation. The APT device features a low-diffraction optical design and a highly efficient 4-stage, closed-loop feedback control system.

The FSO system has been found to exhibit remarkable tracking capabilities, through the integration of multiple sensors and sophisticated algorithms, which are said to enable automatic, fast and accurate acquisition and fine tracking in just 10 minutes. This precision keeps the tracking error within 3 microradians (μrad), resulting in a low average link loss of just 13.7 dB over the 1 km link. Such precision eliminates the need for optical amplification. The FSO system can also achieve bidirectional data rates averaging 9.27 Gbps over the 1 km link, using only commercial transceiver modules.

“This work highlights the potential for achieving FSO using commercially available fibre optical transceiver modules,” said corresponding author Zhenda Xie, professor at the NJU School of Electronic Science and Engineering. Xie added that the effective distance of 1 km may be extended; his team also tested the optical links at up to 4 km, where the average loss increased to 18 dB — likely due to a foggy test environment.

“With better weather conditions and optical amplification, longer FSO can be expected,” he said.

The miniaturised FSO system unlocks the potential for high-speed wireless communication virtually anywhere, making connectivity happen even in the most challenging environments. These devices can be expected to play a pivotal role in the future of FSO networks, offering plug-and-play configurations that can establish high-speed FSO channels in minutes. The team’s innovation thus addresses the growing need for field-deployable, high-speed wireless communication solutions, bridging the connectivity gap in a world where staying connected is more critical than ever.

Image caption: A free-space optical communication experiment involves a pair of FSO devices. One is fixed on the top floor of a building, while the other is loaded on a radio-controlled electric vehicle so that it can move around to vary the distance of the FSO link nodes. Image credit: Liu, Zhang, et al., doi 10.1117/1.APN.2.6.065001.