800 Gb/s/200 m FSO link with a WDM-PAM4 scheme and SLM-based beam tracking technology.

An 800 Gb/s/200 m free-space optical (FSO) link with a wavelength-division multiplexing (WDM)-four-level pulse amplitude modulation (PAM4) scheme and spatial light modulator (SLM)-based beam tracking technology is constructed. To the best of our knowledge, this is the first one that adopts a WDM-PAM4 scheme and an SLM-based beam tracking technology to simultaneously afford a high transmission capacity of 800 Gb/s and resolve the laser beam misalignment problem due to target device movement. By adopting a 16-wavelength WDM-PAM4 scheme, the transmission capacity of the FSO link is considerably enhanced with an 800 Gb/s (50Gb/sPAM4/λ×16λ) total capacity. By deploying an SLM-based beam tracking technology, the laser beam misalignment problem is practically resolved for providing an FSO link with high link accessibility. This demonstrated WDM-PAM4 FSO link fully meets the requirements of high-speed, long-reach, and high-reliability transmissions.