  We demonstrate for the first time a four-node trusted-node-free metro network
configuration with dynamic discrete-variable quantum key distribution DV-QKD
networking capabilities across four optical network nodes. The network allows
the dynamic deployment of any QKD link between two nodes of the network, while
a QKD-aware centralised software-defined networking (SDN) controller is
utilised to provide dynamicity in switching and rerouting. The feasibility of
coexisting a quantum channel with carrier-grade classical optical channels
where both the quantum and classical channels are in the C-band over
field-deployed metropolitan networks and laboratory-based fibres (<10km) is
experimentally explored in terms of achievable quantum bit error rate, secret
key rate as well as classical signal bit error rate. Moreover, coexistence
analysis over multi-hops configuration using different switching scenarios is
also presented. The secret key rate dropped 43% when coexisting one classical
channel with 150 GHz spacing from the quantum channel for multiple links. This
is due to the noise leakage from the Raman scattering into the 100 GHz
bandwidth of the internal filter of the Bob DV-QKD unit. When coexisting four
classical channels with 150 GHz spacing between the quantum and the nearest
classical channel, the quantum channel deteriorates faster due to the
combination of Raman noise, other nonlinearities and high aggregated launch
power causing the QBER value to exceed the threshold of 6% leading the SKR to
reach a value of zero bps at a launch power of 7 dB per channel. Furthermore,
the coexistence of a quantum channel and six classical channels through a
field-deployed fibre test network is examined.
