Robustness of fiber-optic attenuators to 1061-nm sub-nanosecond pulsed laser radiation in quantum key distribution systems

TL;DR

This study experimentally assesses the vulnerability of various fiber-optic attenuators to pulsed laser attacks at 1061 nm, revealing potential security risks for quantum key distribution systems.

Contribution

It provides new insights into the damage thresholds and vulnerabilities of different fiber-optic attenuators under pulsed laser exposure, highlighting security concerns.

Findings

Mechanical and fixed air-gap attenuators resist pulsed laser damage.

MEMS attenuators experience increased attenuation or damage, reducing their effectiveness.

Pulsed irradiation lowers damage thresholds of fixed attenuators, creating potential side-channels.

Abstract

The security of quantum key distribution (QKD) systems relies on the physical integrity of their components. While laser-damage attacks (LDAs) using high-power continuous-wave (cw) lasers have been well studied, the threat posed by pulsed lasers at alternative wavelengths remains underestimated. Here, we experimentally investigated the stability of four types of fiber-optic attenuators under exposure to sub-picosecond pulses at 1061 nm with average power reaching 1 W. Mechanical variable attenuators with blocking elements and fixed air-gap attenuators show resistance to this attack. MEMS-based variable attenuators exhibit increased attenuation or irreversible damage that causes a permanent reduction in attenuation of approximately 3.8 dB. For fixed attenuators with an absorption element, we demonstrate that initial pulsed irradiation significantly lowers the optical damage threshold of the components compared to direct cw attacks. The attenuation reduction achieved is up to 7 dB at a 1 W cw laser at 1550 nm. These results highlight the possibility of establishing a hidden side-channel for eavesdropping attacks and underscore the insufficiency of existing countermeasures against sophisticated LDA scenarios.