Application fields and classification of optical thin films: optical thin films are functional thin films that work by using the effect of thin films on light. Optical thin films can realize spectral transmission, spectral reflection, spectral absorption and light reflection reduction, reflection enhancement, beam splitting, high pass, low pass, narrow band filtering and other functions in changing light intensity. There are many kinds of optical films, which endow optical elements with various performance and play an important or decisive role in realizing the function of optical instruments and affecting the quality of optical instruments.

The traditional optical thin film is an important part of modern optical instruments and various optical devices. By plating one or more thin films on the surface of various optical materials, the light intensity, polarization state and phase change of transmitted or reflected light can be changed by the interference effect of light. The film can be plated on the surface of optical glass, plastic, optical fiber, crystal and other materials. Its thickness can range from several nm to tens or hundreds μ m。 The optical film can obtain good firmness and optical stability, and the cost is relatively low. It hardly increases the volume and weight of the material. Therefore, it is the preferred method to change the optical parameters of the system. It can even be said that without the optical film, there would be no modern optical instruments and various optical devices. In the development of more than two hundred years, optical thin films have formed a complete set of optical theory - thin film optics. Optical thin films have been widely used in various optical devices (such as laser resonators, interference filters, optical lenses, etc.), not only that, its important role in the optoelectronic field is gradually recognized by people.