  Traditionally, photonic crystal slabs can support resonances that are
strongly confined to the slab but also couple to external radiation. However,
when a photonic crystal slab is placed on a substrate, the resonance modes
become less confined, and as the index contrast between slab and substrate
decreases, they eventually disappear. Using the scale structure of the Dione
juno butterfly wing as an inspiration, we present a low-index zigzag surface
structure that supports resonance modes even without index contrast with the
substrate. The zigzag structure supports resonances that are contained away
from the substrate, which reduces the interaction between the resonance and the
substrate. We experimentally verify the existence of substrate-independent
resonances in the visible wavelength regime. Potential applications include
substrate-independent structural color and light guiding.
