“…Bell test, foundation of entanglement science, Multi-path experiments Source that is relatively compact and stable, but with good entanglement visibility and count rates Sagnac sources [248][249][250], Standard BBO (or BiBO) sources [79,245,247,251], Crossedcrystal sources [243,246,359], Review article [244] Bell test -loophole free Source with very high coupling efficiency and very high visibility…”