Optics is the cornerstone of photonics systems and applications. In this module, you will learn about one of the two main divisions of basic optics - geometrical (ray) optics. In the module to follow, you will learn about the other - physical (wave) optics. Geometrical optics will help you understand the basics of light reflection and refraction and the use of simple optical elements such as mirrors, prisms, lenses, and fibers. Physical optics will help you understand the phenomena of light wave interference, diffraction, and polarization; the use of thin film coatings on mirrors to enhance or suppress reflection; and the operation of such devices as gratings and quarter-wave plates.