Pulsed laser attack at 1061 nm potentially compromises quantum key distribution

Abstract

Quantum key distribution systems offer cryptographic security, provided that all their components are thoroughly characterised. However, certain components might be vulnerable to a laser-damage attack, particularly when attacked at previously untested laser parameters. Here, we show that exposing 1550-nm fiber-optic isolators to 1061-nm sub-nanosecond pulsed illumination with 1.16 W average power permanently degrades their isolation at 1550 nm, while their forward transparency is less affected. One experimental sample was exposed to 17-mW average power picosecond attacking pulses that temporarily reduced its isolation below the specified guaranteed minimum value. This indicates a potential security threat in these attacking laser regimes that need to be addressed by improving security analysis for various light-injection attacks.