The most widely used optical component, mirrors are highly polished plane or curved surfaces for reflecting or focusing light. The basic substrate can be coated with single or multiple layers to achieve the desired reflectivity for narrow or broadband applications. Mirrors can be plane, spherical, parabolic or even hot and cold. Mirrors are chosen based on their surface characteristics and the spectral range of the application. They are generally circular, square or elliptical shaped.

Mirror coating materials are chosen based on the need to address a specific region of the spectrum. A popular coating material is Al, because of its broadband coverage and relatively lower cost. An overcoat layer of silicon monoxide is added for further mechanical protection. For applications in the IR and near IR, Au is preferred as it demonstrates a higher reflectance in that band.