Measuring Blackbody Noise in Silica Optical Fibres for Quantum and Classical Communication

Deployment of practical quantum networks, which operate at or near single photon levels, requires carefully quantifying noise processes. We investigate noise due to blackbody radiation emitted into the guided mode of silica single mode optical fibres near room temperature, which to date is under-explored in the literature. We utilise a single photon avalanche detector and lock in detection to measure $\approx$0.1 photons/s/THz ($\approx$-170dBm/THz) at 40{\deg}C near the optically thick limit of 20km in silica fibre. We also measure a coarse spectrum to validate the blackbody behaviour, and observe a prominent anomaly around the 1430nm CWDM channel, likely due to -OH impurities. Though the magnitude of this noise is small, it is additive noise which imposes a fundamental limit in raw fidelity in quantum communication, and a fundamental noise floor in classical communication over optical fibres.