Strong light illumination on gain-switched semiconductor lasers helps the eavesdropper in practical quantum key distribution systems

TL;DR

This paper investigates how strong light illumination raises the temperature of gain-switched semiconductor lasers, causing output fluctuations that can be exploited by eavesdroppers in quantum key distribution systems.

Contribution

It provides a detailed simulation of temperature effects on semiconductor lasers and introduces a modified attack exploiting these effects, along with countermeasures.

Findings

Temperature increase causes large intensity fluctuations

Output intensity decreases with temperature rise

Signal and decoy states become distinguishable due to temperature effects

Abstract

The temperature of the semiconductor diode increases under strong light illumination whether thermoelectric cooler is installed or not, which changes the output wavelength of the laser (Lee M. S. et al., 2017). However, other characteristics also vary as temperature increases. These variations may help the eavesdropper in practical quantum key distribution systems. We study the effects of temperature increase on gain-switched semiconductor lasers by simulating temperature dependent rate equations. The results show that temperature increase may cause large intensity fluctuation, decrease the output intensity and lead the signal state and decoy state distinguishable. We also propose a modified photon number splitting attack by exploiting the effects of temperature increase. Countermeasures are also proposed.