# An Optical Differential Method for Underwater Wireless Communication in Turbid Environments
## 5 Conclusions  
In this study, a novel method, namely, ODCM, is proposed to extend the distance of underwater wireless optical communications in turbid water. The underlying physical reason is explained in theory and demonstrated in experiments. It is found that the extinction coefficient of ODCM is much lower in comparison with that of conventional methods relying on intensity modulations. The stable propagation distance of ODCM could be further extended without relying on intensive light sources, which contrasts with conventional methods, showing a potential for longer communication ranges. To demonstrate superior performance, tests of optical communication in natural water, 3 NTU Formazin solution, and a real river are used to compare the ODCM and intensity modulations. The results show that ODCM can significantly reduce the BER at the same propagation distance or extend the propagation distance for the same BER level of optical signals. As such, this study provides a route to long-distance and stable underwater wireless optical communications. This article primarily examines the performance of ODCM under strong scattering effects. However, in practical underwater environments, many other factors need to be considered, such as turbulence, absorption, and water temperature. It is also worth noting that the detection rate of present commercial color sensors is relatively low. Considering the high-speed detection requirements of underwater optical communication, improving the communication rate of ODCM will require the development of faster color sensors. These would be interesting research topics for our future work. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/photonics12020112/s1](https://www.mdpi.com/article/10.3390/photonics12020112/s1)]([https://www.mdpi.com/article/10.3390/photonics12020112/s1](https://www.mdpi.com/article/10.3390/photonics12020112/s1)). Refs. [31; 32; 33] are cited in Supplementary Materials file. Conceptualization, X.T. and J.W. ; methodology, X.T. and J.W. ; software, X.T. and F.J.; validation, X.T. and J.W. ; formal analysis, X.T., F.J. and J.W. ; investigation, X.T., F.J., H.Y. and [PERSON]; resources, [PERSON] and [PERSON]; data curation, [PERSON], [PERSON] and [PERSON]; writing--original draft preparation, [PERSON] and [PERSON]; writing--review and editing, [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]; visualization, [PERSON] and [PERSON]; supervision, [PERSON]; project administration, [PERSON] and [PERSON]; funding acquisition, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. [PERSON] gratefully acknowledges the General Program of Natural Science Foundation of China (62475065) and the Scientific Research Starting Fund from Hangzhou Dianzi University (KYS045623025, GK239909299001-408). [PERSON] acknowledges the Fundamental Research Funds for the Provincial Universities of Zhejiang (No. GK229909299001-007). Not applicable. Nonetheless. Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request. The authors thank [PERSON] from Everuping Optics Co., Ltd. for the technical support during the secondary development of the spectrometers. The authors declare no conflicts of interest. [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; et al. Gb/s Underwater Wireless Optical Communications Using Series-Connected GaN Micro-LED Arrays. _IEEE Photonics J._**2020**, _12_, 7901210. [CrossRef]
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* _[PERSON] et al. (2024)_ [PERSON]; [PERSON]; [PERSON] Beyond 10 Gbps in Hostile Underwater Optical Wireless Communication Channel Conditions Using Polarisation Division Multiplexing. _J. Lightwave Technol._**2024**, _42_, 4444-4453.