Photonic crystals are materials that have a periodic structure on the scale of the wavelength of light. These materials have unique optical properties, such as the ability to control the flow of light and manipulate its behavior. Photonic crystals have applications in various fields, including telecommunications, sensing, imaging, and energy harvesting. Researchers in this area study the design, fabrication, and characterization of photonic crystals to explore their potential for use in optical devices and systems.