Fully guided polarization entanglement distribution in an existing telecom fiber infrastructure of an institution campus area

We demonstrate the field deployment of a Sagnac interferometer based polarization-entangled photon-pair source centered at the telecom wavelength of 1550 nm with a bandwidth of ~52nm. The source utilizes a periodically poled lithium niobate (PPLN) ridge waveguide, designed for degenerate spontaneous down-conversion. High-fidelity entangled Bell states are measured with sufficient tolerance against temperature and environment that renders the source its utility for practical quantum communication over existing fiber infrastructure. We demonstrate a polarization-entanglement distribution over a 2-km single-mode fiber link within the IIT Delhi campus, while addressing polarization-dependent loss and fluctuations induced by real-world environmental factors that sums up to a total channel loss of ∽ 22 dB. The generated |Φ+⟩ Bell state exhibits an average two-photon interference visibility of ~95%, a fidelity of 91% corresponding to Bell parameter of ~2.58 ± 0.04. We estimate a quantum bit error rate (QBER) of approximately 5%. These results are a contribution towards the realization of practical quantum networks, enabling applications in secure communication, quantum key distribution and distributed quantum information processing over metropolitan fiber infrastructure.