  We report on singular and nonsingular flat bands in a Sierpinski fractal-like
photonic lattice. We demonstrate that the the lowest two bands, being isolated
and degenerate due to geometrical frustration, are nonsingular and thus can be
spanned by a complete set of compact localized states. We experimentally prove
these states to propagate diffractionless in the photonic lattice. Our results
reveal the interplay between geometrical frustration, degenerate flat bands and
compact localized states in a single photonic lattice, and pave the way to
photonic spin liquid ground states.
