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Influence of guided acoustic wave Brillouin scattering on excess noise in fiber-based continuous variable quantum key distribution

We experimentally study the depolarized guided acoustic wave Brillouin scattering in a long-distance telecom single-mode fiber (SMF-28e). It is shown that such a scattering process can introduce excess noise and further degrade the performance of the fiber-based continuous variable quantum key distribution (CVQKD) system where a fiber is utilized as the quantum channel. Based on the experimental results we deduce a lower bound for the extinction ratio of the pulsed light in the time-multiplexing CVQKD protocol.