Thin-film lithium niobate photonic platform for CV-QKD in inter-satellite links: a feasibility study through chip design, characterization, and radiation testing

Abstract Continuous-variable quantum key distribution (CV-QKD) is a promising route to secure inter-satellite optical links, as it integrates naturally with coherent classical communication technology while offering quantum-based security. However, meeting the stringent size, weight, and power constraints of spaceborne payloads requires a photonic integrated platform that combines high-speed, low-noise modulation with low optical losses. Thin-film lithium niobate (TFLN) is uniquely suited to this role thanks to its outstanding electro-optic properties, but its application to CV-QKD has remained unexplored. In this work, we present a feasibility study of a CV-QKD transceiver architecture on a monolithic TFLN photonic integrated circuit (PIC) oriented towards low Earth orbit inter-satellite links. We design the modulation scheme and QKD architecture on a single TFLN PIC, fabricated through a commercial multi-project wafer run, and experimentally characterize its passive and active building blocks. We further report gamma radiation testing of the fabricated chips up to 47 krad, observing no significant degradation in passive performance, RF response, or IQ modulation fidelity. Building on these experimentally measured device parameters, we develop a simulation environment that maps realistic hardware imperfections onto the achievable secret key rate in both fiber and free-space optical channels, obtaining simulated secure key rates in the Mbit/s range at short link distances. These results provide a first hardware-anchored feasibility assessment of CV-QKD on TFLN and outline the design refinements needed to progress towards operational inter-satellite links.