Performance Research for Quantum Key Distribution Based on Real Air-Water Channel

Considering the irregular air-water interface, incident angle, environmental background light and optical attenuation, the system model of quantum key distribution (QKD) based on air-water channel is built. And the influence of wind speed and incident angle on the error rate of system is discussed. Besides, under different attenuation coefficients, the effect of actual incident angle and environmental background light on system performance is studied. The simulations show that when the descending photon passes through the air-water interface, the raise of wind speed leads to an increase in error rate. Similarly, the enlarging of actual incident angle also causes the growth of error rate and shortens the transmission distance of QKD system. Moreover, since the environmental background light can seriously damage the system performance, the QKD experiment should be conducted on cloudy night. With the maximum error rate on cloudy night, the secure transmission distance in clear seawater can reach 252 m, which obviously meets the need of 100 m diving depth for underwater vehicles. In medium seawater and turbid seawater, they are 42 m and 25 m, respectively. Auxiliary means (such as towing buoys) can be used to extend the transmission distance of QKD. Therefore, the QKD system based on air-water channel is feasible, which has certain reference value to expand QKD applications.