Summary
Underwater Optical Communication (UWOC) is a type of FSO communication for underwater applications. The increased density of water compared to air makes challenges such as absorption, scattering, turbidity and distance even greater challenges. Practically this means that distances are highly limited compared to typical underwater acoustic communication (UAC) communication, but UWOC data rates are much higher.[1] UAC systems are typically capable of speeds in the range of kbps over tens of kilometers, while demonstration UWOC systems have shown that transmission rates of up to 1-Gbps over 250 meters underwater are possible, [2] and another system achieved 10 Mbps at a distance of 105m at deep sea depths. [3]
Generally, these systems use 450-550nm blue-green light due to its greater penetration of ocean water, though the ideal wavelength varies depending on the condition of the water, such as the amount of chlorophyll/plankton and turbidity present. [4] This is roughly equivalent to how the color of water will change when it is disturbed. One technique that has been tested is Wavelength Division Multiplexing (WDM), or multiple beams of light of slightly different wavelengths at the same time. [5]
References
[1] Shijie Zhu, Xinwei Chen, Xiaoyan Liu, Guoqi Zhang, Pengfei Tian, Recent progress in and perspectives of underwater wireless optical communication, Progress in Quantum Electronics, Volume 73, 2020, 100274, ISSN 0079-6727
https://doi.org/10.1016/j.pquantelec.2020.100274.
[2] Xiaohe Dong, Kuokuo Zhang, Caiming Sun, Jun Zhang, Aidong Zhang, and Lijun Wang, “Towards 250-m gigabits-per-second underwater wireless optical communication using a low-complexity ANN equalizer,” Opt. Express 33, 2321-2337 (2025)
https://opg.optica.org/oe/fulltext.cfm?uri=oe-33-2-2321
[3] T. Fan, T. Zhou, G. Hu and H. Gu, “Implementation of 105 m Dynamic Underwater Wireless Optical Communication in the Deep Sea,” in IEEE Photonics Technology Letters, vol. 37, no. 18, pp. 1057-1060, 15 Sept.15, 2025, doi: 10.1109/LPT.2025.3580742.
https://ieeexplore.ieee.org/document/11039842
[4] Kuokuo Zhang, Caiming Sun, Wu Shi, Jing Lin, Binghui Li, Weiwei Liu, Danyuan Chen, and Aidong Zhang, “Turbidity-tolerant underwater wireless optical communications using dense blue–green wavelength division multiplexing,” Opt. Express 32, 20762-20775 (2024)
https://opg.optica.org/oe/fulltext.cfm?uri=oe-32-12-20762
[5] Zhang K, Sun C, Shi W, Lin J, Li B, Liu W, Chen D, Zhang A. Turbidity-tolerant underwater wireless optical communications using dense blue-green wavelength division multiplexing. Opt Express. 2024 Jun 3;32(12):20762-20775. doi: 10.1364/OE.521575. PMID: 38859449.
https://pubmed.ncbi.nlm.nih.gov/38859449/
G. Song and J. Xu, “Review on Long-distance Underwater Wireless Optical Communication,” 2021 19th International Conference on Optical Communications and Networks (ICOCN), Qufu, China, 2021, pp. 1-4, doi: 10.1109/ICOCN53177.2021.9563681.
https://ieeexplore.ieee.org/document/9563681