Anti-Reflective Coating with Multiple Layers

Application ID: 19279

Anti-reflective coatings are frequently used in optical systems to reduce the amount of stray light produced when a beam of light crosses from one medium into another medium with a different refractive index. The simplest example of an anti-reflective coating is a quarter-wavelength layer, in which the thickness of a monolayer dielectric film is adjusted to be one fourth of the optical wavelength. Although a single-layer coating can reduce the reflectance to zero for light at a specific wavelength and angle of incidence, the reflectance can be substantially larger for other wavelengths. One possible solution is to use a multilayer coating that gives consistently low reflectance over a wider spectral band.

In this tutorial, light crosses a boundary between two media with different refractive indices at normal incidence. The reflectance of two different multilayer coatings is compared over a wide spectral range: a quarter-quarter coating (two layers), and a quarter-half-quarter coating (three layers). The quarter-half-quarter coating is shown to have more consistently low reflectance across most of the visible spectrum.

This model example illustrates applications of this type that would nominally be built using the following products: