  We demonstrate experimentally the feasibility of continuous variable quantum
key distribution (CV-QKD) in dense-wavelength-division multiplexing networks
(DWDM), where QKD will typically have to coexist with several co- propagating
(forward or backward) C-band classical channels whose launch power is around
0dBm. We have conducted experimental tests of the coexistence of CV-QKD
multiplexed with an intense classical channel, for different input powers and
different DWDM wavelengths. Over a 25km fiber, a CV-QKD operated over the
1530.12nm channel can tolerate the noise arising from up to 11.5dBm classical
channel at 1550.12nm in forward direction (9.7dBm in backward). A positive key
rate (0.49kb/s) can be obtained at 75km with classical channel power of
respectively -3dBm and -9dBm in forward and backward. Based on these
measurements, we have also simulated the excess noise and optimized channel
allocation for the integration of CV-QKD in some access networks. We have, for
example, shown that CV-QKD could coexist with 5 pairs of channels (with nominal
input powers: 2dBm forward and 1dBm backward) over a 25km WDM-PON network. The
obtained results demonstrate the outstanding capacity of CV-QKD to coexist with
classical signals of realistic intensity in optical networks.

Quantum Physics