  Entanglement is an invaluable resource for fundamental tests of physics and
the implementation of quantum information protocols such as device-independent
secure communications. In particular, time-bin entanglement is widely exploited
to reach these purposes both in free-space and optical fiber propagation, due
to the robustness and simplicity of its implementation. However, all existing
realizations of time-bin entanglement suffer from an intrinsic postselection
loophole, which undermines their usefulness. Here, we report the first
experimental violation of Bell's inequality with "genuine" time-bin
entanglement, free of the postselection loophole. We introduced a novel
function of the interferometers at the two measurement stations, that operate
as fast synchronized optical switches. This scheme allowed to obtain a
postselection-loophole-free Bell violation of more than nine standard
deviations. Since our scheme is fully implementable using standard fiber-based
components and is compatible with modern integrated photonics, our results pave
the way for the distribution of genuine time-bin entanglement over long
distances.
