Array of superconducting nanowire single photon detectors resolving the number of photons in a weak optical pulse

Determining the precise number of photons in a weak optical pulse is of crucial importance for imaging, computing or communication applications that use single photons or few photons to increase the performance of classical techniques. Single photons or pair of photons can for instance be used to enhance the resolution of optical imaging techniques or to transmit information with ultimate security using quantum cryptography. In order to maintain this performance gain in such applications, the exact number of photons must be measured and monitored. In this contribution we present a method to measure the number of photons in an optical pulse by using 7 superconducting nanowire single photon detectors. Since a single SNSPD is not sensitive to the number of incoming photons, the optical signal multiplexing is necessary to measure photon correlations among the channels and thus reconstruct the input photons statistics. The readout and counting of the photon arrivals is performed with a fast multi-channel Asynchronous-Correlated-Digital-Counter (ACDC) implemented in the Programmable Logic (PL) of a Xilinx ZYNQ-7020 SoC device. The test of the technique has been performed coupling a weak laser via a fiber multiplexer to an array of individually fiber-coupled detectors.