Single-photon interference and router-control in a long-distance Sagnac interferometer

A novel scheme to realize stable single-photon interference and router-control is demonstrated in this report. Phase difference between clockwise and counter-clockwise single-photons was controlled by time-division phase modulation in an optic fiber Sagnac[1] loop. Due to the annular geometric configuration of the Sagnac loop, clockwise and counter-clockwise single-photons traveled the same optical path and had the same slowly-varied phase drifts, which were automatically compensated. Furthermore, clockwise and counter-clockwise single-photons encounter the same polarization mode dispersion, which was also automatically compensated at the exit port of the Sagnac interferometer.