Fig. 1. Experimental setup for generating and characterizing the broadband correlated/entangled photon pairs. (a) Generation of broadband correlated/entangled photon pairs. (b) Single-photon spectrum of correlated photon pairs. (c) Correlation property. (d) Energy-time entanglement. VOA, variable optical attenuator; BS, beam splitter; OPM, optical power meter; PC, polarization controller; PBS, polarization beam splitter; PPLN, periodically polarized lithium niobate; ISO, isolator; TBF, tunable band-pass filter; SNSPD, superconducting nanowire single photon detector; TDC, time-to-digital converter; UMZI, unbalanced Mach–Zehnder interferometer.

Fig. 2. Broadband property of the source. (a) Single-photon spectrum. (b) Raman photon spectrum in the fiber system.

Fig. 3. Results of correlated properties. (a) Single-side counts under different pump powers at paired ITU channels C44 and C48. (b) CARs between paired ITU channels C44 and C48 under different pump powers. Inset is a typical result of the coincidence measurement and the applied 300 ps time windows. (c) CARs and CCs of photon pairs from eight paired ITU channels.

Fig. 4. Results of the two-photon interference of photon pairs from paired ITU channels C44 and C48. (a) Three peaks when α = 0 and β = 0. (b) Three peaks when α = 0 and β = π. (c) Two-photon interference curves.