Quantum communication uses the quantum state as an information source to achieve the effective transmission of the information of quantum state carries. It has the advantages of high security, high transmission speed, and large communication capacity and is thus a hotspot in the current communication field. However, when an equivalent optical signal is transmitted underwater, it is inevitably affected by environmental factors, resulting in the degradation of transmission performance. Sea ice is one of the important factors that affect the transmission of optical quantum signals underwater. It is composed of freshwater ice crystals, brine bubbles, and bubbles containing salt. When an optical quantum signal is transmitted underwater, the bubbles, brine bubbles, and other microbial particles in sea ice absorb and scatter the optical signal, seriously interfering with the transmission of the signal and resulting in reduced communication performance. The propagation, reflection, and absorption of optical quantum signals in sea ice are affected by the particles and sol organics condensed in the sea ice. However, the influence of sea ice on the performance of underwater quantum communication channels has rarely been reported. Therefore, it is of great significance to analyze the extinction characteristics of sea ice as a whole according to the absorption and scattering characteristics of each component of sea ice and study the influence of sea ice with different density and salinity on link attenuation, channel utilization, and the bit error rate and bit rate of a quantum key distribution system.

Sea ice is composed of bubbles, brine bubbles, and other particles. To study the influence of sea ice on the performance of underwater quantum communication channels, this paper analyzes the absorption and scattering characteristics of each component of sea ice. Subsequently, on the basis of the absorption and scattering characteristics of sea ice with different density and salinity, it explores and simulates the relationships of sea ice parameters with the extinction coefficient. Then, according to the extinction characteristics of sea ice with different density and salinity, a constant incident wavelength is adopted, and the relationships of sea ice parameters with link attenuation and channel utilization are determined and simulated experimentally. Finally, the paper examines the effects of sea ice with different density and salinity on the bit error rate and bit rate of a quantum key distribution system and implements data simulation. The theoretical analysis and simulation results can provide a reference for the design of underwater quantum communication in sea ice environments.

Under the same incident wavelength, the extinction coefficient of sea ice increases with sea ice density and sea ice salinity, and it is more markedly affected by the change in sea ice salinity (Fig. 2). When the transmission distance is short and sea ice salinity is small, the link attenuation caused by sea ice is also small. As the transmission distance of the optical quantum signal and sea ice salinity increase, link attenuation increases rapidly (Fig. 4). As sea ice density rises, the extinction effect on the quantum state of the light becomes more obvious, which leads to a decrease in channel utilization (Fig. 5). Since the scattering of light by sea ice changes the polarization of photons constituting the qubit and causes bit errors, the bit error rate of the underwater quantum system increases with sea ice salinity (Fig. 8). The bit rate of the key distribution system is affected by sea ice salinity and transmission distance. When sea ice salinity is small and transmission distance is short, the system bit rate changes slowly. When sea ice salinity is large and transmission distance is long, the attenuation of the optical quantum signal is serious, and the value of the bit rate decreases rapidly (Fig. 10).

According to the extinction characteristics of sea ice, this paper determines the relationships of sea ice density and sea ice salinity with link attenuation, channel utilization, and the bit error rate and bit rate of the quantum key distribution system. Furthermore, it comparatively analyzes the influence of sea ice on the performance of underwater quantum communication under different parameters. The simulation results show that the link attenuation and the bit rate of the underwater quantum key distribution system tend to decrease as transmission distance and sea ice salinity or sea ice density increase. Moreover, the utilization rate of the quantum communication channel and the system bit rate decrease to varying degrees. In comparison, the change in sea ice salinity interferes more strongly with communication quality and influences the channel parameters more saliently. Therefore, the effects of sea ice density and sea ice salinity on the quantum state of light, especially the effects of sea ice salinity, must be fully considered when underwater quantum communication is conducted.