  We propose a quantum access network based on multicore fiber (MCF) to scale
up the number of users in quantum key distribution (QKD) networks. The MCF is
used as feeder fiber and single core single mode fibers (SSMFs) are used as
drop fibers. Quantum signals (QSs) are integrated with classical signals (CSs)
in both MCF and SSMFs to save deployment cost since access networks are cost
sensitive. Due to the integration, spontaneous Raman scattering (SRS) and
intercore crosstalk (ICXT) are the main impairment sources to QKD. To alleviate
the noise, we propose a core and wavelength assignment scheme (CWAS) that a
dedicated core of MCF is used to transmit QSs and the wavelengths of QSs are
set lower than those of upstream signals. Also, we demonstrate that wavelength
time division multiplexing (WTDM) is suitable for QSs which are required to
support large number of quantum users, since WTDM can realize higher secure key
rate (SKR) than time division multiplexing (TDM) and require lower cost than
wavelength division multiplexing (WDM). Finally, the proposed quantum access
network is verified experimentally. The experiment results are consistent with
our analysis. The properties of SRS in the proposed architecture are shown in
the experiments through the quantum bit error rates (QBERs) in different
experimental case, which verifies the superiority of the proposed CWAS. Also,
the characteristics of the SKRs prove that the number of receivers has a great
impact on the performance of QSs using WTDM.
