  Weyl fermions1 do not appear in nature as elementary particles, but they are
now found to exist as nodal points in the band structure of electronic and
classical wave crystals. Novel phenomena such as Fermi arcs and chiral anomaly
have fueled the interest of these topological points which are frequently
perceived as monopoles in momentum space. Here, we demonstrate that generalized
Weyl points can exist in a parameter space and we report the first observation
of such nodal points in one-dimensional photonic crystals in the optical range.
The reflection phase inside the band gap of a truncated photonic crystal
exhibits vortexes in the parameter space where the Weyl points are defined and
they share the same topological charges as the Weyl points. These vortexes
guarantee the existence of interface states, the trajectory of which can be
understood as "Fermi arcs" emerging from the Weyl nodes.
