Polarisation drift compensation in 8 km-long Mach-Zehnder fibre-optical interferometer for quantum communication

In this paper, the polarisation drift between the arms of an 8 km-long fibre-optical Mach-Zehnder interferometer is experimentally stabilised, while simultaneously compensating the phase fluctuations. The single photons are wavelength-multiplexed with three classical channels, which are used as feedback for the control systems. Two of these channels are used for the active polarisation control systems, while the other is used to phase-lock the interferometer. Long-term stabilisation of the singlephoton visibility, when the polarisation control is used, is demonstrated.