Objective Laser underwater transmission has many advantages, such as high transmission rate, low time delay and high precision. When light is sent underwater, it is affected by the absorption and scattering of particles in the water, as well as different types of turbulence, which further limits the wide application of light transmission systems. There is a large vorticity region near the bubble, and the movement of the bubble will produce turbulence. The more bubbles there are, the greater the number of bonds of the corresponding fluid, so that the bubbles contained in the fluid are more likely to break into small-scale bubbles, thus increasing the instability of the fluid and generating turbulence. Due to the wake of ships, underwater vehicles, wave breaking and other factors will produce bubbles, which will have an important impact on the performance of underwater optical transmission system. On the basis of previous studies, the underwater wireless optical transmission system under the influence of bubble scattering is studied in this paper.

Methods A simulation model of light transmission under the influence of bubble scattering is proposed in this paper. Compared with the traditional Monte Carlo model, the model introduces random variation of scattering coefficient and changes the random step size of photon motion according to the amount of bubble in water. Based on the idea of simulation research, the transmission characteristics of laser in the bubble are experimentally studied, and the energy ratio between the left and right sides of the average received light intensity is analyzed.

Results and Discussions The results show that the received light intensity distribution obtained by the model is in good agreement with the experiment. With the change of the position of bubbles, the probability density distribution of the received light intensity hardly changes significantly, and the probability of receiving light intensity reaches the maximum at the position with greater than the average light intensity ( I/I_0 > 1 ) (Fig.4). With the increase of the number of bubbles, the peak probability density of received light intensity gradually transitions from a position greater than the average light intensity to a position less than the average light intensity (Fig.5). In addition, the change of the energy ratio of the left and right sides of the average received light intensity was also analyzed, and it was found that with the increase of the number of bubbles, the received light intensity energy ratio showed a trend of first increasing and then decreasing, but was always less than 1(Fig.6).

Conclusions A simulation model of underwater light transmission under the influence of bubbles is established in this paper. The model is based on the random variation of the scattering coefficient under the influence of bubbles, and the random step of photon transmission is changed according to the amount of bubbles in water. By comparing the results obtained from the simulation model with the experiments, it is found that by changing the maximum scattering coefficient under the influence of the bubble and the random step size in the photon collision process, the received light intensity distribution obtained from the simulation model can be well consistent with the experiment, indicating that the bubble will have an important impact on the performance of light transmission by changing the scattering coefficient and scattering times of light in water. In addition, the change of the energy ratio between the left and right sides of the average received light intensity is also studied. It is found that with the increase of the number of bubbles, the energy ratio increases first and then decreases, but it is always less than 1. The research results of this paper can provide a useful reference for the study of underwater light transmission characteristics in the real bubble environment.