Various optical thin film devices made of the optical functional thin film have become an indispensable part of the optical systems and optical instruments.  Its application has developed from traditional optical instruments to astrophysics, aerospace, laser, electrical, communications, materials, construction, biomedical, infrared physics, agriculture, and many other technical fields.  Let’s take a look at some classifications of optical films.  

1. Traditional optical film and new optical film  

(1) Traditional optical films  

Traditional optical films are based on the interference of light.  A light wave is a kind of electromagnetic wave, according to its wavelength can be divided into infrared, visible light and ultraviolet, etc., when the light wave is projected to the object, a part of it is reflected on the surface, the rest of the refraction into the object, a part of it is absorbed into heat energy, the rest of the transmission.  Different materials have different reflection, absorption, and transmission properties of light, optical film has been used as the material for the light this performance, and according to the actual needs of manufacturing.  

Traditional optical films make use of this property of materials to produce specific behavior for light.  Traditional optical films include reflection film, antireflection film, filter film, nano-optical film, polarization film, spectroscopic film, and phase film.  

(2) New optical films  

With the development of modern science and technology, especially laser technology and information optics, optical thin films are not only used in pure optical devices but also widely used in photoelectric devices and optical communication devices.  With the development of modern information optics, optoelectronics, and photonics technology, the requirements for long life, high reliability, and high strength of optical thin film products are becoming higher and higher.

Thus, a series of new optical thin films and their preparation technologies are developed, and comprehensive solutions are provided to solve the problems faced by the industrialization of the optical thin films.  It includes high-intensity laser, diamond, and diamond-like film, soft X-ray multilayer film, solar selective absorption film, and optical communication film, etc.  

2. Commonly used optical films  

(1) antireflection film  

Antireflection film is the most widely used optical film, which can reduce the reflectivity of the optical surface and improve its transmittance.  For a single wavelength, the theoretical reflectivity can fall to zero.  For the visible spectrum, the reflectivity can be reduced to 0.5% or even lower to ensure adequate transmittance and extremely low stray light for a complex system consisting of multiple lenses.  There is no modern optical device that has not been reduced.  Due to its very low reflectivity and bright surface color, modern glasses in daily life are generally coated with an anti-reflection film.  

(2) high reflection film  

It reflects most of the incoming light energy.  When the dielectric film reactor is selected, the reflectivity of the optical film can be increased with the increase of the number of film layers due to its very low loss.  This highly reflective film is common in laser fabrication and laser applications.  

(3) Basic optical film  

The basic optical film refers to the realization of optical transmission, optical reflection, optical absorption, and changes in the polarization state or phase of light, can be used for a variety of reflection films, anti-reflective films, and interference filter films, it gives optical elements a variety of performance, to ensure the quality of optical instruments play a decisive role.  

(4) Spectral spectroscopic film  

Incident light can be part of the spectrum of energy transmission, the other part of the spectrum of energy reflection.  The reflection of longwave energy and transmission of short wave energy is called short wave pass cut-off filter film;  The transmission of longwave energy and short wave energy reflection is called long-wave pass cut-off film.  

They can be used to divide a beam of light into multiple beams of different colors.  For example, if a beam of light is divided into three primary colors, red, green, and blue, any kind of color light can be obtained by the combination of these three colors.  This kind of color film is indispensable in the photoelectric color industry, such as color photography, color TELEVISION, color projection, color printing, and other fields.  

(5) Optical properties of the transformable film  

The optical properties of the changeable film refer to the material under the influence of the external environment to produce a change of light response, under certain external conditions (heat, light, electricity), so that it can change the color and restore, this color-changing film is a kind of optical functional materials with broad application prospects.  

It can be seen that optical thin films play an important role in almost all characteristics of optical devices.  There would be no modern optical system without optical films.  With the development of science and technology, the combination of optical film and optoelectronic film, and the combination of energy, environmental protection, and other new technologies, in addition, to constantly creating new concepts, and new applications will continue to produce new industries, promote the development of optical film towards depth and wider range.