Fig. 2
From: Boosting the secret key rate in a shared quantum and classical fibre communication system
Simulation of the normalised secret key rate as a function of the intrinsic error for parallel (Par.) and high-dimensional (Hi-D) encoding. Different colours represent the number of spatial modes used from \(N=2\) (light-grey) to \(N=32\) (orange). In the Hi-D case (dashed-lines) a multicore or few-mode fibres is used to encode the quantum states. A BB84 decoy states protocol with two mutually unbiased bases is implemented for the simulations58. Parameters used are fibre link \(d=7.9\) km (loss \(=3.75\) dB), detectors efficiency \({\eta }_{{\rm{d}}}=0.6\), receiver efficiency \({\eta }_{{\rm{bob}}}=0.85\). In the parallel encoding scheme (full-lines), the same protocol, with same parameters, is used for all the different modes or cores independently. The shown secret key rate is normalised on the system repetition rate \(\nu\)
