Characterisation of single-mode fiber coupled (on/off) single photon detectors: detection efficiency, non-paralizable deadtime, dark counts. Characterisation of single-mode fiber coupled (on/off) single photon detectors (e.g. the ones based on InGaAs/InP-SPAD and SNSPD). Specifically: (a) traceable measurement of the detection efficiency at 1550 nm; (b) characterisation of dark count; (c) jitter (upon request, setup requires customisation). Setup for the characterisation of the polarization sensitivity of the detection efficiency under validation. Typical detectors should be SMF28 dingle mode fiber coupled. Wavelengths other than 1550 nm available on request (contact us). Detector should be free runnig. For gated detectors please contact us.