Trade study of aperture size, adaptive optics and multiple spatial modes for a polarization entanglement QKD system over a 30 km maritime channel

Transmitting a beam through the atmosphere over long distances can be a challenging problem. Factors from the channel, such as atmospheric turbulence causing beam wander and distortions to the wavefront, or the optical design can change the loss induced in the channel. This work simulates a quantum key distribution system implementing the BB84 protocol with entangled photons operating over a 30 km maritime channel using one, four, and nine spatial modes. For the cases of multiple spatial modes, atmospheric turbulence increases the channel cross talk, resulting in an increase in the noise for each channel. To compensate for distortions in the wavefront, adaptive optics at the transmitter or receiver are used to pre- or post-correct the wavefront.