Three-dimensional network photonic crystals via cyclic size reduction/infiltration of sea urchin exoskeleton

Many naturally occurring solids possess periodic structures that give rise to visible photonic crystal properties,([1]) commonly termed structural colors. Some stunning examples are butterfly wings (one-dimensional, 1D), ([2]) abalone shells (1D),([3]) sea-mouse spines (two-dimensional, 2D),([4]) and natural opals (three-dimensional, 3D).([5]) Exploitation of other periodic natural structures, is however limited by the inherently large size scale and the low dielectric contrast of the materials. Furthermore, these generally more complex geometries are a challenge to model correctly in order to obtain correct band diagrams. Here we report the development of a high fidelity cyclic size reduction and infiltration scheme, and apply it to a sea urchin exoskeleton to successfully fabricate a high dielectric contrast 3D photonic crystal exhibiting a stop band in the mid-IR range. The band structure of the exoskeleton is modeled using level set mathematics and agrees well with the experimental reflectivity exhibited by the 3D bicontinuous tellurium network of the replicated urchin.