Vulnerabilities of quantum key distribution systems in the visible range

In this paper, we investigate spectral vulnerabilities in quantum key distribution systems arising from the use of shorter-wavelength radiation in the 400–800 nm range, with particular focus on the induced photorefraction attack (IPA). Crucial elements influenced by the IPA include various types of both phase and intensity modulators, and we consider different scenarios and their implications. Through combined theoretical and experimental analysis, we demonstrate that optical components commonly used as countermeasures in the telecom band (1000–2100 nm) exhibit significantly reduced effectiveness at shorter wavelengths. The efficiency of IPA is shown to increase as the wavelength decreases, posing a substantial threat to phase-modulation-based QKD protocols. We analyze the impact of IPA across different QKD architectures and assess the feasibility of potential countermeasures under realistic implementation scenarios. Our results highlight the necessity of broadband security evaluations and wavelength-aware component design in future QKD systems.