Second-Order Correlation Measurement for Single-Photon Metrology

The critical aspect in the field of single-photon metrology is to measure the detector efficiency with the lowest possible uncertainty and reproducibility. The developments in quantum technologies have paved the way for applications such as quantum imaging and quantum information processing, including quantum computing and quantum communications proving superior to the conventional technologies currently in use. Superconducting Nanowire Single-Photon Detectors (SNSPDs) are one of the key elements in these applications and are preferred over similar devices due to their better performance parameters. The instrumentation used for characterizing single-photon detectors must be precise and reliable so that no optical event gets missed. Here, we present an optical setup based on the 2nd-order correlation measurement, developed to characterize single-photon detectors at visible to near-infrared wavelengths. Each device used in the setup has been thoroughly characterized, and their response under different operating conditions has been studied. In the setup, a few photons generated by attenuating a laser are split by a 50:50 fiber beam splitter and sent to two single-photon detectors. A correlation card measures the coincidences.