100G FSO field trial with transmitter power adaptability using a LoRa feedback channel

Abstract

The popularity of free-space optics (FSO) communications is rising as a key enabler for widespread communications since it can provide fiber-like connectivity to regions where fiber deployment is not feasible and radio-frequency (RF) technologies cannot comply with the bandwidth requirements. However, the reliability of FSO links is severely affected by fluctuations in the received optical power caused by weather instability, atmospheric turbulence, and pointing errors. In this work, we propose an adaptive power pre-compensation system enabled by a low-cost, long-range (LoRa) RF feedback link. We experimentally demonstrate this system in a 1.8 km field trial supporting 100 Gbps coherent FSO transmission under approximately 10 dB of slow-fading over a 16 h period. Our results show a considerable reduction of up to 5 dB in the average dynamic range of the receiver and substantial improvement in the link reliability (7% on average) when compared with an estimated fixed power transmission. Further reliability or data-rate improvements can also be achieved with joint optimization of the FEC overhead and the adaptive power transmission scheme.