Amplification pulse signals a single-photon detector based on an avalanche photodiode
Roman Halyts, Петро Шпатар, Yurii Yaremchuk · 2024
The technology of quantum cryptography, based on the quantum properties of light, allows a random sequence of bits to be transmitted over an unprotected communication channel in such a way that an attacker's interference in the transmission process creates additional noise in the channel and is detected by legitimate users. One of the important elements of a quantum system is a single-photon detector. The closest to solving this problem is a device for recording single photons using avalanche photodiodes (APD) [1 - 6]. In this work, a scheme for amplifying current pulses flowing through a single-photon detector is proposed, using a charge-sensitive amplifier Amptek A250. The noise characteristics of the Amptek A250 amplifier are such that its contribution to detector noise is negligible. After amplification, the pulses are fed to the inputs of the comparators. The amplitude discrimination threshold of the first is selected above the level of the amplifier's own noise. The amplitude discrimination threshold of the second comparator is chosen so that the speed of pulse counting at the output of the first comparator is n times greater than at the output of the second comparator. From the outputs of the comparators, pulses are fed to the input of the microcontroller. When the microcontroller calculates a given number of N pulses, a corresponding signal for the DAC is formed at its output, which converts the digital signal into a control voltage for the power source of the avalanche photodiode. The developed device allows to increase the quantum efficiency of registration up to 48%.