Simulation of a submarine to submarine QKD system

Due to the absorption of water, communication between two parties submersed below the water is normally performed with acoustic waves. However, with the need for higher data rates, the use of RF or optical frequencies is needed. Currently optical wavelengths have been demonstrated for classical communication over short distances. For these short distances, if a large amounts of data needs to be transmitted securely, it is not feasible for both parties to return to the surface to exchange, and it can be assumed that a third party Eve, is located in the channel trying to gather information. The solution is to use quantum key distribution (QKD) to generate the secure key, allowing the parties to continuously encrypt and transmit the data. It is assumed the BB92 protocol using pairs of entangled photons generated from a spontaneous parametric down conversion (SPDC) source of Type-II. By using entangled photons, Eve is not able to gain information without being detected. In this work, the beam propagation through a horizontal oceanic channel is studied for various distances ranging from 10m to 100m at visible wavelengths. The secure key rates are then calculated assuming that a low-density parity check (LDPC) error correction code is used for information reconciliation, as well as the maximum distance that a QKD protocol can be implemented for a submarine environment.