Fiber-optic power limiter device based on carbon nanotubes

TL;DR

The paper tackles the susceptibility of quantum key distribution (QKD) to high-power light-injection attacks by introducing a passive optical fuse based on a carboxymethylcellulose film with dispersed single-walled carbon nanotubes (CMC-CNT). The device, placed at a fiber junction, irreversibly increases attenuation above $50~\mathrm{mW}$ at $1550~\mathrm{nm}$ and can trigger a fiber fuse at $1$–$5~\mathrm{W}$, effectively disconnecting the link under attack. Demonstrations show compatibility with both phase-encoded and polarization-encoded QKD systems, providing protection without degrading normal operation but exhibiting notable sample-to-sample variability in attenuation rise. The work offers a low-complexity, integrable hardware countermeasure against light-injection attacks, with future work focusing on improving repeatability and scalable integration into QKD transmitters.

Abstract

We experimentally demonstrate a power limiter based on single-walled carbon nanotubes dispersed in a polymer matrix. This simple fiber-optic device permanently increases its attenuation when subjected to 50-mW or higher cw illumination at 1550 nm and initiates a fiber-fuse effect at 1 to 5 W. It may be used for protecting quantum key distribution equipment from light-injection attacks. We demonstrate its compatibility with phase- and polarisation-encoding quantum key distribution systems.

Figures (12)

• Figure 1: The design of optical fuse (not to scale). The sample of CMC-CNT is between the ferrules of the connectors inserted into a standard bulkhead adapter. Diameter of the fiber $a =125~\micro\meter$, ferrule diameter $b = 2.5~\milli\meter$, sample thickness $h = 5~\micro\meter$.
• Figure 2: Attenuation spectrum of sheet CMC-CNT film at normal incidence, measured with Perkin-Elmer Lambda 950 spectrophotometer.
• Figure 3: Experimental setup. LD1, laser diode; VOA, variable optical attenuator; OPM, optical power meter; BS, beamsplitter; DUT, device under test; LD2, seed laser diode; EYDFA, erbium-ytterbium-doped fiber amplifier.
• Figure 4: Attenuation of samples 1--6 after their irradiation by increasing amount of power. A spark at the end of the curve denotes the sample initiating the fiber-fuse effect, destroying its fiber pigtail and ending the test.
• Figure 5: Attenuation of samples exposed to power up to $2.6~\milli\watt$.