A practical method for determining the dead time in a single-photon avalanche diode with a weak laser beam

Dead time refers to a time in which the single photon detector cannot detect a new photon due to the effects caused by the incoming photon detection and the reset process. Due to the importance of dead time in limiting the detection frequency of single photon avalanche detectors and limiting the exchange rate in various systems, such as quantum key distribution, measuring this characteristic in single photon detectors is essential. In the proposed method of this research, A weak continuous laser beam can use to determine the dead time. An FPGA chip is proposed to measure the dead time in single photon detectors. The suggested FPGA model XC3S400 belongs to the Spartan family of Xilinx company.