Quantum key distribution with spectral amplitude coding OCDMA for a multiple access network

This study presents the design and analysis of a hybrid multi-user quantum key distribution (QKD) system utilizing spectral amplitude coding optical code division multiple access (SAC-OCDMA) encoding techniques. By assigning unique optical codes to each user, SAC-OCDMA enables spontaneous, asynchronous data transmission without any strict synchronization, which makes it scalable and flexible for quantum networks. In the architecture, each user’s quantum signal, initially prepared as weak coherent pulses and encoded using phase or polarization bases, is further spectrally sliced by a SAC-OCDMA encoder in a zero-based cross-correlation code. The physical impairments, comprising spontaneous Raman scattering, four-wave mixing, and crosstalk, were modeled and analyzed. We report a maximum secret key rate of ∼10 5 bps over a transmission distance of ∼58km . Furthermore, our analysis demonstrates that careful selection of launch power, simultaneous users, code weight, and spectral bin width is necessary for optimizing the trade-off between multi-user capacity and security performance. In comparison with wave division multiplexing QKD, which has much better spectral efficiency but strict channel allocation, the flexibility and asynchronous access to secure communication of our OCDMA-QKD design with zero cross-correlation coding are more aligned with the needs of quantum security.