In practical applications, communication between underwater platforms typically employs super low frequency/very low frequency (SLF/VLF) with narrow transmission bandwidths and insufficient security. Underwater laser communication has become a research hotspot due to its potential to provide higher transmission bandwidths and smaller transmission delay. However, adopting a Gaussian beam as a carrier of laser communication signals for underwater communication is limited by oceanic turbulence, which weakens the beam intensity and causes beam wander, beam expansion, and light intensity fluctuation to restrict the distance of underwater laser communication. To this end, we propose to utilize a Hermite-Gaussian beam for laser communication in oceanic turbulence. While this technique has been demonstrated in atmospheric turbulence, the mean square beam width, Rayleigh range, and turbulence distance in oceanic turbulence have not been reported. Therefore, our paper aims to build a beam transmission model in oceanic turbulence and analyze the mean square beam width, Rayleigh range, and turbulent distance. Finally, a more effective solution is provided for underwater laser communication technology, which can improve communication quality and extend the communication distance, thereby enabling more effective underwater exploration and resource development.

The research methodology involves the study on propagation properties of partially coherent Hermite-Gaussian beams in oceanic turbulence. Our study begins by developing an intensity analysis model of Hermite-Gaussian beams in oceanic turbulence based on the extended Huygens-Fresnel principle. Then, the mean square beam width, Rayleigh range, and turbulent distance of Hermite-Gaussian beams in oceanic turbulence are derived. The expressions are obtained by the analytical approach based on the proposed intensity analysis model. Finally, the simulation analysis of the mean square beam width, Rayleigh range, and turbulent distance of Hermite-Gaussian beams in oceanic turbulence is conducted. The proposed theoretical model is adopted for analyzing the propagation of Hermite-Gaussian beams in seawater. The relationship between the parameters such as the Rayleigh range and the oceanic turbulence parameters is studied, and a reasonable physical interpretation is given. We provide a theoretical framework for analyzing the propagation properties of partially coherent Hermite-Gaussian beams in oceanic turbulence. The results can be leveraged to improve the performance of underwater laser communication systems.

We investigate the effect of oceanic turbulence parameters on the mean square beam width, Rayleigh range, and turbulent distance of Hermite-Gaussian beams in oceanic turbulence. The results indicate that the mean square beam width increases with the rising mean square temperature dissipation rate. Additionally, the mean square beam width decreases with the dissipation rate of turbulent kinetic energy and decreases to a greater extent when the parameter w takes smaller values. Meanwhile, the larger parameter w determines the larger mean square beam width when salinity dominates. We also find that the mean square beam width increases with the transmission distance. The coherence length has less influence on the beam width and a larger coherence length results in a smaller beam width. The order of the Hermite-Gaussian beam also influences the beam width, and a higher order corresponds to a larger beam width. The Rayleigh range of the beam decreases with the mean square temperature dissipation rate and the relevant parameter w of temperature and salinity and increases with the turbulent kinetic energy dissipation rate. Finally, the turbulent distance decreases with the increase in the mean square temperature dissipation rate and the parameter w, and rises with the turbulent kinetic energy dissipation rate. Our findings have important implications for the design and optimization of underwater optical communication systems.

Our paper presents a study on the propagation properties of partially coherent Hermite-Gaussian beams in oceanic turbulence. We derive the expression for the cross spectral density function of the Hermite-Gaussian beam by the extended Huygens-Fresnel principle. We then investigate the effects of oceanic turbulence parameters and optical parameters on the Hermite-Gaussian beam transmission characteristics. The results show that the mean square beam width of the Hermite-Gaussian beam increases with the mean square temperature dissipation rate and the relative parameters of temperature and salinity, while it decreases with the dissipation rate of turbulent kinetic energy. In addition, the higher order Hermite-Gaussian beam means a larger mean square beam width, and both the Rayleigh range and the turbulent distance increase with the rising beam order. These findings suggest that higher-order Hermite-Gaussian beams are more resistant to turbulent perturbations and can lead to longer effective communication distances. Our study is significant for underwater laser communication research and provides insight into the optimal design parameters for communication systems operating in oceanic turbulence.