介绍一种稳定的长距离单光子干涉仪,即光纤Sagnac单光子环形干涉仪,其平衡结构有效地补偿了由于光纤长度随时间缓变带来的相位涨落和光纤本身形状随时间缓变引起的偏振态涨落。在Sagnac环形干涉仪中通过分时相位调制实现了1550 nm波长27km单光子干涉,对比度大于90％,进一步的讨论表明该单光子干涉仪可用于长距离稳定的单光子路由和量子保密通信。 A stable long-distance single-photon interferometer, a fiber-optic Sagnac single-photon ring interferometer, is introduced. Its balanced structure effectively compensates for the phase fluctuation caused by the slow change of the fiber length with time and the gradual change of the fiber shape with time Polarization fluctuations. In the Sagnac ring interferometer, 27km single-photon interference with a wavelength of 1550 nm and a contrast ratio of more than 90% has been achieved by time-phased phase modulation. Further discussions show that the single-photon interferometer can be used for stable single-photon routing and quantum secure communication over long distances.