Single-photon Sagnac interferometer

We present the first experimental demonstration of the optical Sagnac effect at the single-photon level. Using a high quality guided-wave heralded single- photon source at 1550 nm and a fibre optics setup, we obtain an interference pattern with net visibilities up to (99.2 $\pm$ 0.4%). On the basis of this high visibility and the compactness of the setup, the interest of such a system for fibre optics gyroscope is discussed.