Single-channel 48-Gbit/s DP PSK Y-00 quantum stream cipher transmission over 400- and 800-km SSMF.

A record-large product of data rate and transmission distance in quantum-noise-assisted cipher systems for physical layer security of fiber-optic transmission was demonstrated. The cipher system is based on symmetric-key direct-data encryption utilizing signal masking by quantum (shot) noise. The encryption is achieved by 216-level phase randomization of quadrature phase-shift keying data signal, resulting in 48-Gbit/s dual polarization Y-00 cipher with 218 phase levels. Successful transmission of the Y-00 cipher over 400- and 800-km standard single-mode fibers was achieved without significant negative impact on transmission quality. The product of the data rate and distance was 40 Gbit/s (net rate) × 800 km = 32,000 Gbit/s·km. The system achieves masking of 217 phase levels by shot noise, which promises irreducible and unchanged security based on the quantum nature of coherent light.