  We present a method based on a time domain simulation of wave propagation
that allows studying the optical response of a broad range of dielectric
photonic structures. This method is particularly suitable for dealing with
complex biological structures. One of the main features of the proposed
approach is the simple and intuitive way of defining the setup and the photonic
structure to be simulated, which can be done by feeding the simulation with a
digital image of the structure. We also develop a set of techniques to process
the behavior of the evolving waves within the simulation. These techniques
include a direction filter, that permits decoupling of waves travelling
simultaneously in different directions, a dynamic differential absorber, to
cancel the waves reflected at the edges of the simulation space, a
multi-frequency excitation scheme based on a filter that allows decoupling
waves of different wavelengths travelling simultaneously, and a
near-to-far-field approach to evaluate the resulting wavefield outside the
simulation domain. We validate the code and, as an example, apply it to the
complex structure found in a microorganism called Diachea leucopoda, which
exhibits a multicolor iridescent appearance.
