  We propose a waveguide-cavity coupled system to achieve the routing of
photons by the phases of other photons. Our router has four input ports and
four output ports. The transport of the coherent-state photons injected through
any input port can be controlled by the phases of the coherent-state photons
injected through other input ports. This control can be achieved when the mean
numbers of the routed and control photons are small enough and require no
additional control fields. Therefore, the all-optical routing of photons can be
achieved at the single-photon level.
