  The topic of photonic topological insulators and scattering-protected edge
states bridges concepts from condensed matter physics and electromagnetics, and
necessitates understanding the Berry potential and related concepts. These
notes are an attempt at a moderately self-contained introduction to the topic,
including two detailed photonic examples drawn from the literature. We made
these notes in the process of trying to understand this topic ourselves, and we
are posting this material in the spirit of helping other researchers start to
understand this material. We claim no novelty in the material or its
presentation.
