Fig. 1. Internal structure diagram and modulation bandwidth measurement results of micro-LED device^[26]. (a) Structure diagram of micro-LED; (b) spectral measurement results; (c) normalized frequency response under different driving currents

Fig. 2. Test results for the system employing 16-QAM and OFDM technology^[31]. (a) Error vector magnitude (EVM) and constellation diagram; (b) subcarrier signal-to-noise ratio and constellation diagram; (c) EVM of 2.4 Gbit/s 16-QAM OFDM data after underwater transmission over 1.7 m; (d) relationship between subcarrier and signal-to-noise ratio along with corresponding constellation diagrams

Fig. 3. Schematic diagrams of conventional underwater wireless optical communication systems employing Gaussian beams and adaptive links utilizing circularly symmetric self-focusing Airy beams^[52]

Fig. 4. Concept of an underwater orbital angular momentum-multiplexing optical communication link and intensity distributions of Gaussian beams and orbital angular momentum beams under different conditions^[59]. (a) Concept of an underwater orbital angular momentum-multiplexing optical communication link; (b) intensity distributions of the Gaussian beam and OAM l=+1, +3 beams under different conditions including tap water, water current, scattering, and turbulence; (c) eye diagrams after transmission through l=+3 OAM channel

Fig. 5. Underwater wireless optical communication experimental system based on 8th-order quadrature phase shift keying and coherent heterodyne detection technology^[79]

Fig. 6. Underwater wireless optical communication prototype and sea test certificate developed by WHOI, USA^[96]

Fig. 7. Engineering prototype and sea trial certificate for wireless optical communication in water system developed by IFREMER, France^[99]

Fig. 8. Japan’s “1 Gbit/s×100 m underwater optical wireless communication” deep-sea experimental platform and sea trial prototype^[100]

Fig. 9. Architecture for sea trial verification of high-speed underwater optical communication machines^[93]

Fig. 10. LED-based underwater wireless optical communication engineering prototype developed by the Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, and its sea trial verification

Fig. 11. Real-time monitoring system for subsea pipelines based on the integrated LED transceiver for deep-sea wireless blue-green optical communication technology

Fig. 12. Vision of an integrated communication, navigation, and timing (CNT) network for future air-space-ground-sea convergence^[110]