  Due to their compatibility to existing telecom technology, continuous
variable (CV) weak coherent state protocols are promising candidates for a
broad deployment of quantum key distribution (QKD) technology. We demonstrate
how an existing simulation framework for modelling classical optical systems
can be utilized for simulations of weak-coherent CV-QKD links. The quantum
uncertainties for the measured characteristics of coherent signals are modelled
in the electrical domain by shot noise, while a coherent signal in the optical
domain is described by its quadrature components. We simulate various
degradation effects such as attenuation, laser RIN, Raman noise (from classical
channels in the same fibre), and device imperfections and compare the outcome
with analytical theory. Having complemented the physical simulation layer by
the post-processing layer (reconciliation and privacy amplification), we are
able to estimate secure key rates from simulations, greatly boosting the
development speed of practical CV-QKD schemes and implementations.
