Abstract
Topological photonics, an emerging field in photonics, is now receiving much attention not only due to
its fundamental interests but also potential applications in integrated photonics. The concept of band topology
originally developed in condensed matter physics provides a novel route for controlling light
wave in periodic optical systems such as photonic crystals. Here, we try to give readers a rough idea of
what topological photonics is. Starting with a brief overview of the field, we will explain the fundamental
concept “without” using any equations. Then, we will introduce the three possible topological
two-dimensional photonic crystals. Among them, valley photonic crystal, which can be simply realized
based on semiconductor nanophotonics, will be discussed in detail.
