Fig. 2

Experimental system of 40-user fully connected QKD network. (a) Energy–time entangled photon pairs are generated through spontaneous four wave mixing (SFWM) based on a silicon waveguide. Arrayed waveguide grating is used to demultiplex the entangled photon pairs by wavelengths into 100-GHz-spaced ITU channels. After demultiplexing, the corresponding combinations of wavelength channels are multiplexed together by 100 GHz dense wavelength division multiplexing (DWDM) components and distributed to users in different subnets. The numbers on the DWDMs represent the subscripts of the corresponding wavelength channels. Each subnet receives six wavelength channels. These photons are randomly distributed to the users by a passive beam splitter. In each user, normal and anomalous dispersion components are placed at two paths, followed by two NbN superconducting nanowire single-photon detectors (SNSPDs). The arrival time of photons can be used for key generation and security test based on symmetric dispersive optics QKD. (b) Mono-color pump light of the quantum light source is set at 1545.32 nm, which is the central wavelength of ITU channel C40. Generated signal and idler photons with correlated wavelength channels are symmetrically distributed around the frequency of pump light. Subscripts of wavelengths with opposite numbers correspond to a correlated wavelength channel pair for a specific entanglement resource; corresponding ITU channels are indicated below wavelength symbols. Five correlated wavelength channel pairs (shown in green) are used to support five subnets. The other 10 correlated wavelength channel pairs (shown in orange) are used to connect users between subnets