Quantum Key Distribution High-Count-Rate CMOS SPAD Detector for Ground Segement

The main bottleneck in Quantum Key Distribution (QKD) systems is the maximum count rate of available single-photon detectors, which limits the number of secure keys distributed per unit time. Therefore, the main parameter to be improved for a single-photon detector designed for a QKD link is its maximum count rate. Moreover, in space-based QKD services, the optical link between the satellite and the ground station will use faint pulse photon sources at GHz pulse repetition sent from LEO platforms. To fulfil these requirements, the Quantum Key Distribution High-Rate Detector (QKD-HRD) Predevelopment project, funded and cooperated by the European Space Agency, has started. This project focuses on the development of the four silicon SPAD detector arrays fabricated in CMOS technology for 800 nm wavelength detection. Together with the detector arrays, the reception electronics and the QKD demonstration setup are under preparation. Both the detector arrays and the reception electronics device, based on the Wave-Union (WU) and Equivalent Coding Line (ECL) Field-Programmable Gate Array (FPGA) Time-to-Digital Converter (TDC), will be capable of reaching 2GSa/s of sampling rate. The demonstration setup, based on the Electro-Optic Modulators (EOM), polarizers, amplifiers, and the FPGA high-speed transceivers, will generate the single photon key for testing the QKD protocols. The project aims to develop a system for receiving a high-speed secure key with a bit error rate (BER) as low as possible. In this paper, we will describe the current state of the project (including QKD systems, CMOS SPAD detectors and TDC design), highlighting its main advantages.