  Classical optical communications may be still the main communications
technology for the foreseeable future, so integration of the quantum
communication network with existing classical optical communication network is
necessary because existing telecommunications infrastructure will be shared.
This means multiplexing of quantum key distribution (QKD) and strong classical
data signals, delivering quantum signals and classic signals in one fiber.
Optical splitters are employed to access each user in a gigabit-capable passive
optical network (GPON). In a 4-user network the splitter adds at least 6 dB of
optical loss to the quantum channel, a 64-user network the splitter adds 18 dB
of optical loss to the quantum channel. The optical splitters restrict the
transmission distance and performance of QKD. We propose a new integration
program of QKD and GPON based on wavelength-division multiplexing (WDM). At the
optical splitting point, we use filters to separate the quantum signals and
bypass the optical splitter, avoiding losses produced by the optical splitters.
This increases the counting rate of the quantum signals states and the signal
to noise ratio (SNR) improves, so a higher key generation rate and a longer
transmission distance can be obtained with QKD.
