Verification of calibration methods for determining photon-counting detection efficiency using superconducting...

In recent years several ways to radiometrically calibrate optical fiber-coupled detectors have been developed. However, fiber-coupled calibration methods for single photon detectors have not been compared by national metrology institutes in order to validate their equivalence or traceability to the international systems of units yet.. Here, we present the comparison of radiometric calibration methods traceable to a NIST cryogenic radiometer at the 'few-photon' level. The calibration methods are based on metrology grade optical power meters. The expanded (k = 2) relative standard uncertainties of the calibration methods for the detection efficiency are of the order of 0.5%. However, the results changed relatively by 10% with a different set of optical fibers and mating connectors. These results stress the importance of fiber-core dimensions and fiber-connector repeatability.