A switch activated by a single control photon for routing a single target photon from either of two switch inputs to either of two switch outputs. The device is based on a single quantum emitter, such as an atom, coupled to a fiber-coupled, chip-based optical micro-resonator. A single reflected control photon toggles the switch from high reflection to high transmission mode, with no additional control fields required. The control and target photons are both in-fiber and practically identical, for compatibility with scalable architectures for quantum information processing.