An optical film is one or more layers of film that are plated on the surface of an optical component by changing the surface features of the optical component. It may be a metal film, a dielectric film or a combination of these two types of films. Optical film is an indispensable part of various advanced optoelectronic technologies. It not only improves system performance, but also is a necessary means to meet design goals. Optical film applications and various aspects of optical systems, including laser systems, optical communications, The main optical thin film devices, such as light display, light storage, etc., include a reflective film, an anti-reflection film, a polarizing film, an interference filter, a beam splitter, and the like.
First, the definition of optical film
An optical dielectric material consisting of a thin layered medium that propagates light through an interface. The application of optical thin films began in the 1930s. Optical thin films have been widely used in the fields of optics and optoelectronics to manufacture various optical instruments. The preparation strip requires high and fine parts.
The optical film is defined as a thin and uniform dielectric film layer attached to the surface of the optical device during the propagation path, and the characteristics of reflection, transparency, and polarization when the dielectric layer is layered. It achieves all the special forms of light, such as total transmission of light in one or more bands, or total reflection or polarization separation of light.
Optical films are ubiquitous in our lives, from precision and optical equipment, display devices to optical film applications in everyday life; for example, glasses, digital cameras, household appliances, or security on banknotes Technology can be called an extension of optical film technology applications. If there is no optical film technology as the basis for development, modern optoelectronics, communication or laser technology will not be able to make progress, which also shows the importance of research and development of optical film technology.
Optical film refers to plating or coating one or more layers of dielectric film or metal film or a combination of these two types of films on an optical element or a separate substrate to change the transmission characteristics of light waves, including light transmission. Reflection, absorption, scattering, polarization, and phase changes. Therefore, the transmittance and reflectivity of the surface of the components of different wavelength bands can be modulated by appropriate design, and the light of different polarization planes can also have different characteristics.
In general, the production methods of optical films are mainly divided into dry and wet production processes. The so-called dry type means that no liquid appears in the whole process. For example, vacuum evaporation is to heat the solid raw material with electric energy in a vacuum environment, and after sublimation into a gas, it adheres to the surface of a solid substrate to complete the coating. Processing. The golden, silver or metallic packaging film that is seen in daily life is a product that is manufactured by dry coating. However, in the actual mass production considerations, dry coating applications are less than wet coating. Wet coating is generally practiced by mixing ingredients with various functions into a liquid coating, applying it to a substrate in different processing methods, and then drying and solidifying the liquid coating to form a product.
Second, the principle of thin film interference
1, the volatility of light
In the 1860s, American physicist Maxwell developed the theory of electromagnetics, pointing out that light is an electromagnetic wave that has made the theory of fluctuations quite perfect.
It is known from the wave-particle duality of light that light is electromagnetic waves like radio waves, X-rays, and rays, but their frequencies are different. The relationship between the wavelength λ, the frequency u, and the propagation rate V of the electromagnetic wave is:
V=λu
Since electromagnetic waves of various frequencies are equal in velocity in vacuum, electromagnetic waves of different frequencies have different wavelengths. The high frequency has a short wavelength and the low frequency has a long wavelength. For comparison, the wavelengths (or frequencies) of radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and rays can be sequentially arranged into a spectrum, which is called an electromagnetic spectrum.
In the electromagnetic spectrum, the longest wavelength is a radio wave, and the radio wave is divided into a long wave, a medium wave, a short wave, an ultrashort wave, and a microwave depending on the wavelength. Followed by infrared, visible and ultraviolet light, these three parts are called optical radiation. Of all the electromagnetic waves, only visible light can be seen by the human eye. The wavelength of visible light is between about 0.76 microns and 0.40 microns, accounting for only a small fraction of the electromagnetic spectrum. Again X-rays. The electromagnetic wave with the shortest wavelength is y-ray.
Since light is an electromagnetic wave, in the process of propagation, it should be characterized by its characteristics—interference, diffraction, polarization, and so on.
2, thin film interference
The film can be a transparent solid, a liquid or a thin layer of gas sandwiched between two pieces of glass. The incident light is reflected by the upper surface of the film to obtain a first beam of light, and the refracted light is reflected by the lower surface of the film, and is refracted by the upper surface to obtain a second beam of light which is separated from the same side of the film by the same incident vibration. , is coherent light, and belongs to the amplitude interference. If the light source is an extended light source (surface light source), interference can only be observed in a specific overlap region of the two coherent beams, so it is localized interference. For a planar film whose two surfaces are parallel to each other, the interference fringes are localized at infinity, usually by means of a converging lens in the focal plane of the image; for the wedge-shaped film, the interference fringes are localized in the vicinity of the film.
Experiments and theories have proved that interference fringes can only be produced when two columns of light waves have a certain relationship. These relationships are called coherent conditions. The dry conditions of the film include three points: the two beams have the same frequency; the beam waves have the same vibration direction; the phase difference between the two beams remains constant.
The optical path difference formula of thin film interference two-phase dry light is:
Δ=ntcos(α) ± λ/2
Where n is the refractive index of the film; t is the film thickness at the point of incidence; α is the angle of refraction within the film; λ/2 is due to the two interfaces of the two coherent beams at different properties (one is the light-diffusing medium to the light-dense The additional optical path difference caused by the reflection of the medium and the other is the optically dense medium to the light-diffusing medium. The principle of thin film interference is widely used in the inspection of optical surfaces, precision measurement of tiny angles or lines, preparation of anti-reflection films and interference filters.
Light is radiated by changes in the state of motion of atoms or molecules in the light source. Each atom or molecule emits a wave of light, which is only a short column, lasting about 1 billion seconds. For two independent light sources, The three conditions for generating interference, especially the same phase or constant phase difference, are not easy to satisfy, so two independent general light sources cannot form a coherent light source. Not only that, even light emitted by different parts of the same light source will generally not interfere because they are emitted by different atoms or molecules.
3, optical film characteristics classification
The main optical thin film devices include reflective films, anti-reflective films, polarizing films, interference filters and spectroscopes. They have been widely used in national economy and national defense construction, and have received increasing attention from scientists and technicians. For example, the use of an anti-reflection film can reduce the luminous flux loss of a complex optical lens by a factor of ten; the use of a mirror with a high reflection ratio can double the output power of the laser; the use of an optical film can improve the efficiency of the silicon battery and stability.
The simplest optical film model is a smooth, isotropic, uniform dielectric film. In this case, the optical properties of the optical film can be studied using the interference theory of light. When a beam of monochromatic light is incident on the optical film, multiple reflections and refractions occur on its two surfaces. The directions of the reflected and refracted light are given by the law of reflection and the law of refraction. The amplitude of the reflected photo-refracted light The size is determined by the Fresnel formula.
Optical films can be classified into: reflective film, antireflection film/antireflection film, filter, polarizer/polarizing film, compensation film/phase difference plate, alignment film, diffusion film/sheet, according to their use classification, characteristics and application. Brightening film / prism sheet / concentrating sheet, shading film / black and white glue, etc. Related types are optical grade protective films, window films, and the like.
The characteristics of the optical film are: the surface is smooth, the interface between the layers is geometrically divided; the refractive index of the film layer can jump at the interface, but it is continuous in the film layer; it can be a transparent medium or an absorption Medium; either normal or uniform. The actual application of the film is much more complicated than the ideal film. This is because: when prepared, the optical properties and physical properties of the film deviate from the bulk material, the surface and interface are rough, resulting in diffuse reflection of the beam; the interpenetration between the layers forms a diffusion interface; due to the growth of the layer , structure, stress and other reasons, the formation of a variety of anisotropy of the film; the film layer has a complex time effect.
Reflective films can generally be divided into two categories, one is a metal reflective film, and the other is an all-dielectric reflective film. In addition, there is a metal dielectric reflective film that combines the two to increase the reflectivity of the optical surface.
Generally metals have a large extinction coefficient. When the light beam is incident on the metal surface by the air, the amplitude of the light entering the metal is rapidly attenuated, so that the light energy entering the inside of the metal is correspondingly reduced, and the reflected light energy is increased. The larger the extinction coefficient, the faster the attenuation of the light amplitude, and the less the light energy entering the metal interior, the higher the reflectivity. People always choose metals with large extinction coefficient and stable optical properties as metal film materials. The thin metal material commonly used in the ultraviolet region is aluminum. Aluminum and silver are commonly used in the visible region, and gold, silver and copper are commonly used in the infrared region. In addition, chromium and platinum are also commonly used as film materials for special films. Since materials such as aluminum, silver, and copper are easily oxidized in the air to lower the performance, they must be protected by a dielectric film. Commonly used protective film materials are silicon oxide, magnesium fluoride, silicon dioxide, aluminum oxide, and the like.
The metal reflective film has the advantages of simple preparation process and wide working wavelength range; the disadvantage is that the light loss is large and the reflectance is not high. In order to further improve the reflectance of the metal reflective film, a plurality of dielectric layers having a certain thickness may be plated on the outer side of the film to form a metal dielectric reflective film. It should be pointed out that the metal dielectric film increases the reflectivity of a certain wavelength (or a certain wave region), but destroys the characteristics of the neutral reflection of the metal film.
Editor: Li Jie
AVS, AVSS, TXL, GXL, UL2464,UL1015,UL1007 normally used for car alarm wiring. JST, Dephi, Molex, and Chinese equipvalent part canbe assembly in the harness. Yacenter expands oversea markets, such as Europe, America,Janpan, etc. Owing to the rapid development, Yacenter has been awarded as [UL, CE, TS"certificate.
Any technical question, inquiry price, feel free to communicate with us.
Car Alarm Wiring,Car Alarm Wire Harness,Automobile Car Alarm Wire Harness,Car Stereo Alarm Wiring Harness
Dongguan YAC Electric Co,. LTD. , https://www.yacentercn.com