  We present a source of states for Quantum Key Distribution (QKD) based on a
modular design exploiting the iPOGNAC, a stable, low-error, and
calibration-free polarization modulation scheme, for both intensity and
polarization encoding. This source is immune to the security vulnerabilities of
other state sources such as side channels and some quantum hacking attacks.
Furthermore, our intensity modulation scheme allows full tunability of the
intensity ratio between the decoy and signal states, and mitigates patterning
effects. The source was implemented and tested at the near-infrared optical
band around 800 nm, of particular interest for satellite-based QKD. Remarkably,
the modularity of the source simplifies its development, testing, and
qualification, especially for space missions. For these reasons, our work paves
the way for the development of the second generation of QKD satellites that can
guarantee excellent performances at higher security levels.
