  Photons in optical networks can be used in multi-path interferometry and
various quantum information processing and communication protocols. Large
networks, however, are often not free from defects, which can appear randomly
between the lattice sites and are caused either by production faults or
deliberate introduction. In this work we present numerical simulations of the
behaviour of a single photon injected into a regular lattice of beam-splitting
components in the presence of defects that cause perfect backward reflections.
We find that the photon dynamics is quickly dominated by the backscattering
processes, and a small fraction of reflectors in the paths of the
beam-splitting array strongly affects the percolation probability of the
photon. We carefully examine such systems and show an interesting interplay
between the probabilities of percolation, backscattering and temporary
localization. We also discuss the sensitivity of these probabilities to lattice
size, timescale, injection point, fraction of reflectors and boundary
conditions.
