  We show a setup for characterising the efficiency of a single-photon-detector
absolutely and with a precision better of 1%. Since the setup does not rely on
calibrated devices and can be implemented with standard-optic components, it
can be realised in any laboratory. Our approach is based on an
Erbium-Doped-Fiber-Amplifier (EDFA) radiometer as a primary measurement
standard for optical power, and on an ultra-stable source of spontaneous
emission. As a proof of principle, we characterise the efficiency of an
InGaAs/InP single-photon detector. We verified the correctness of the
characterisation with independent measurements. In particular, the measurement
of the optical power made with the EDFA radiometer has been compared to that of
the Swiss Federal Office of Metrology using a transfer power meter. Our
approach is suitable for frequent characterisations of high-efficient
single-photon detectors.
