A wide range of optical thin film devices made from optical functional films have become an important and indispensable part of optical systems and optical instruments. Its applications have developed from traditional optical instruments to astrophysics, aerospace, lasers, electricians, communications, materials, architecture, biomedicine, infrared physics, agriculture and many other technical fields.

They are divided into: basic optical films, light control films, optical film materials

1、Basic optical film

Basic optical films are films that can realize spectral transmission, spectral reflection, spectral absorption and change the polarization state or phase of light, and can be used for various reflective films, transmission enhancement films and interference filters, which give optical components a variety of performance and play a decisive role in ensuring the quality of optical instruments.

1.1 Anti-reflective film (transmissive film)

A reflective film is a functional film used to reduce reflection losses from the surface of an optical element. It can be made up of single or multi-layer systems. Single-layer films have zero reflectance at a given wavelength, while multi-layer films have practically zero reflectance at a given wavelength. The type of reflective film used in an application is dependent on a number of factors such as substrate material, wavelength range, desired characteristics and cost, depending on the conditions and the application.

a. Single-layer reflective films

To reduce the consumption of light reflection and increase the transmission of light, a layer of reflective film is often deposited on the surface of the glass. The principle is the phenomenon of light interference. As long as the refractive index of the film is less than the refractive index of the glass substrate, it can achieve the light's anti-reflective effect.

b. Multi-layer reflective film

Multi-layer reflective film is mainly to improve the shortcomings of single-layer reflective film, to further improve the effect of reflective film, so the use of measures to increase the number of layers of film.

1.2 Reflective film

Reflective film is the opposite of retroreflective film in that it is required to reflect back most or almost all of the incident light. Reflective films are deposited on optical instruments, lasers, waveguides, cars, lamps and mirrors. There are two types of reflective film: metallic and dielectric. a. Metallic reflective film

Metal reflective films have a high reflectivity and a certain absorption capacity. Highly reflective metal films are only used where there are no special requirements for the absorption loss of the film.

b. Dielectric reflective film

The absorption loss of metal high reflective film is large, in some applications, such as multi-beam interferometer, high quality laser reflective film, it requires the deposition of low absorption, high reflection of the full media high reflective film.

2、Light control film

Light control film is divided into sunlight control film, low emissivity film, optical properties can be converted into three kinds of film .

2.1, sunlight control film

In the glass coated with a layer of optical film, so that the glass of the visible part of the sunlight has a high transmittance, and the infrared part of the sunlight has a high reflectivity, and the ultraviolet part of the sunlight has a high absorption rate. It will be made into sun-coated curtain wall glass, you can ensure that there is enough brightness in the building during the day, etc. 2.2, low emissivity film

The surface of the glass is coated with a low emissivity film, called low emissivity film, commonly known as thermal insulation film, which has a high reflectivity of infrared light.

2.3, optical properties can be changed film

Optical properties can be changed film refers to the material under the influence of the external environment to produce a change in response to light, in certain external conditions (heat, light, electricity), so that it changes colour and can be restored, this colour change film is a class of optical functional materials with broad application prospects.

3、Optical film materials

3.1, metals and alloys

Metals and alloys are more widespread film, with high reflectivity, cut-off bandwidth, good neutrality, small polarization effect and absorption can be changed, etc., in some special-purpose film system, they have a particularly important role.

3.2. Compounds (dielectrics)

Compounds are important and widely used in optical films, mainly: halides, oxides, sulfides and selenides.

3.3, Semiconductors

Semiconductor materials are transparent in the near and far infrared regions and are an important class of optical film materials. The most common semiconductor materials used in optical films are silicon and germanium.