On the Optimization of Underwater Quantum Key Distribution Systems with Time-Gated SPADs

Abstract: In this paper, we study the effect of various transmitter and receiver parameters on the quantum bit error rate (QBER) performance of underwater quantum key distribution. We utilize a Monte Carlo approach to simulate the trajectories of emitted photons transmitting in the water from the transmitter towards receiver. Based on propagation delay results, we first determine a proper value for bit period to avoid the intersymbol interference as a result of possible multiple scattering events. Then, based on the angle of arrival of the received photons, we determine a proper field-of-view to limit the average number of received background noise. Finally, we determine the optimal value for the single photon avalanche diode (SPAD) gate time in the sense of minimizing the QBER for the selected system parameters and given propagation environment.