  The structure of the cuticle of arthropods consists of layers of
microfilamentary chitin particles. The layers are stacked one on top of the
other realizing a helical (Bouligand helix) pattern. This structure generates
optical phenomena such as structural colors and birefringence that produce a
metalic or iridescent appearance, polarization upon reflection and optical
activity. We model the anisotropic optical responses of the cuticle of
arthropods using the Photonic package to obtain the macroscopic dielectric
tensor of a constitutive layer in the Bouligand helix. We find that its
anisotropy depends on the shape of the chitin particles, their reticular
arrangement and their filling fractions. As a main result, we obtained a
cuticle model with tunable reflectance band gaps that are very sensitive to
geometrical parameters such as the angle $\theta$ that controls the helix
pitch. We can explain the structural colors in terms of the reflectance band
gap induced by the modulation of the anisotropy mediated by $\theta$, instead
of following the usual approach that consider multiple arrangement of layers
pairs with different thickness and optical properties.
