Datacom-Blind Shortwave QKD: Enhancing Security for Short-Reach Links

In recent years, the practical application of quantum key distribution (QKD) in telecom networks has been extensively explored, with
numerous field trials successfully demonstrating its feasibility. The urgency for implementing QKD is increasingly underscored by the
rapid expansion of datacenters, which are transitioning from traditional perimeter security models to a zero-trust model, where no
internal resource is inherently trusted. The datacenter interconnects, typically characterized by an optical budget of around 6 dB and
limited fiber reach, allows for the adoption of shortwave QKD schemes. By operating at the border of the visible-light and nearinfrared regions, shortwave QKD takes advantage of highly efficient silicon SPADs, circumventing the dead-time limitations inherent
in InGaAs SPADs while sustaining key exchange over lossy channels, thanks to their lower dark count rate. Shortwave QKD has
primarily been demonstrated in free-space scenarios. However, its application in fiber-based telecom networks holds significant
promise for enhancing security in these rapidly evolving datacenter environments.
We experimentally demonstrate datacom-blind QKD operation at 852 nm over a 1-km short-reach optical interconnect, co-existing
with a 100-Gb/s LAN-WDM link across four unattenuated classical O-band channels. Our results indicate that QKD performance
remains unaffected by Raman noise, and only minimal spectral filtering is required for co-existence. Additionally, we explore the
impact of few-mode transmission on the shortwave quantum channel using standard telecom fiber and compare its performance to
a 1550-nm QKD setup. Our findings contribute to the advancement of shortwave QKD in datacenter environments, emphasizing its
robustness and compatibility with existing high-speed data transmission infrastructure.