The invention relates to a single photon detector device for detecting an optical signal comprising an optical fiber and at least one nanowire, wherein the optical fiber comprises a core area and a cladding area and is designed to conduct the optical signal along an optical axis, wherein, with respect to the optical axis, a first area of the optical fiber is an entrance area for the optical signal and a second area of the optical fiber is a detector area, and wherein the nanowire becomes superconducting at a predetermined temperature and is designed in the superconducting state to generate an output signal as a function of the optical signal. It is provided that in the detector area of the optical fiber the nanowire extends essentially along the optical axis of the optical fiber. A single photon detector device is thus provided which has a simple structure, a high efficiency, a high detection rate and a high spectral bandwidth.