A 400-Gb/s WDM-PAM4 OWC System Through the Free- Space Transmission With a Water-Air-Water Link

Abstract

A 400-Gb/s wavelength-division-multiplexing (WDM) four-level pulse amplitude modulation (PAM4) optical wireless communication (OWC) system through a 200-m free-space transmission with either an 8.8-m piped water-air-piped water link or a 6.5-m turbid water-air-turbid water link is attainably constructed. Incorporating PAM4 modulation with an 8-wavelength WDM scheme greatly increases the total transmission rate of the WDM-PAM4 OWC system to 400 Gb/s (50 Gb/s/λ × 8 λs). By employing doublet lenses in free-space transmission, a laser beam reducer/expander and a reflective spatial light modulator (SLM) with an angle expander through the water-air-water link, high bit error rate performance and acceptable PAM4 eye diagrams are obtained. Using a reflective SLM with an angle expander not only adaptively adjusts the laser beam, but also effectively solves the marine engineering problems. This demonstrated WDM-PAM4 OWC system outperforms existing OWC systems through free-space transmission with an air-water-air link due to its ability to resolve the practical engineering problems in actual marine environments.