 Plane wave expansion method

The Plane Wave Expansion (PWE) method is a mathematical technique often used in the fields of electromagnetics, photonics, and solid-state physics to solve wave propagation problems in periodic structures. This method is particularly useful for analyzing structures such as photonic crystals, diffraction gratings, and resonant cavities. ### Key Concepts of the Plane Wave Expansion Method: 1. **Periodic Structures**: PWE is best suited for systems that exhibit periodicity in one or more dimensions.