What Is Optical Thin Film?

- Feb 22, 2019-

What is Optical thin film?


Principle of optical thin film


Optical film refers to its thickness can be compared to the wavelength of light, followed by the light through its effect. In particular, the upper and lower surfaces reflect and transmit light.


Optical thin film is defined as: involved in the process of the propagation path of light, adhesion in the optical device thickness thin and uniform dielectric film on the surface of the layer, through the layered medium membrane layer reflection, through shot (passbook) and polarization characteristics, in order to achieve what we want in one or multiple wavelengths of light within the scope of all through or light reflection or separation and so on various special form of polarized light.


The characteristics of optical film are: The surface is smooth and the interface between the film layers is geometrically segmented. The refractive index of the film can jump at the interface, but it is continuous in the film. It can be a transparent medium or an absorbing medium. It could be normal or it could be non-uniform. The actual film is much more complicated than the ideal film. This is because: at the time of preparation, the optical and physical properties of the thin film deviate from the bulk material, and its surface and interface are rough, resulting in diffuse scattering of the light beam; The diffusion interface is formed by the mutual permeation of film layers. Because of the growth, structure and stress of the film, the anisotropy of the film is formed. Film layer has complex time effect. Different materials have different properties of reflection, absorption and transmission to light. Optical film is made by using the properties of materials to light and according to actual needs.


Traditional applications of optical thin films


Optical film can be divided into reflective film, anti-reflection film, filter film, optical protective film, polarizing film, spectroscopic film and phase film by application. Antireflective film is the most widely used optical film, it can reduce the reflectivity of optical surface and improve its transmission. For a single wavelength, the theoretical reflectivity can be reduced to zero and the transmission is 100%. For the visible spectrum, the reflectance can be reduced to 0.5% or less to ensure sufficient transmission and very low stray light for a complex system consisting of multiple lenses. There is no modern optical device that does not undergo reflection reduction. Due to its extremely low reflectivity and bright surface color, modern people in the daily life of glasses are generally coated with antireflective film.


High-reflecting film


Most of the incident light energy can be reflected back. When a dielectric film reactor is used, as the loss of the film is very low, the reflectivity can be continuously increased (approaching to 100%) with the continuous increase of the number of film layers. This kind of high reflection film is necessary in laser manufacture and laser application.


Energy spectroscopic film


Part of the incident light energy can be transmitted, another part of the reflection into two beams of light, according to coating online understanding, the most commonly used is T:R=50:50 spectroscopic film.


Spectroscopic film


The energy of part of the spectrum of the incident light can be transmitted, and the energy of another part of the spectrum can be reflected. The long-wave energy reflected and short-wave energy transmitted is called short-wave through cut-off filter; The long-wave energy transmission and short-wave energy reflection is called the long-wave cutoff filter. They can be used to separate a beam of light into different colors.


Bandpass filter


A filter that allows light to pass through only one spectral band, which may be broad or rather narrow. Narrow strip filter is widely used in optics, medicine, criminal investigation, communication, biochemistry and so on. Ultra-narrow band filters have been successfully applied to manufacturing intensive DWDM in optical communication, which promotes the development of optical communication. The most recent and successful use of wideband pass filters is in the manufacture of low-radiation glass, which can be used to develop building window glass that reflects energy and can penetrate sunlight. Tubu online that this rising energy costs today, will develop into a large industry.


Typical applications of new optical thin films


With the development of modern science and technology, especially laser technology and information optics, optical thin film is not only used in pure optical devices, but also widely used in optoelectronic devices and optical communication devices. With the development of modern information optics, optoelectronic technology and photonic technology, the requirements for the long life, high reliability and high strength of optical thin film products are becoming higher and higher, thus a series of new optical thin film and its preparation technologies have been developed, and a comprehensive solution has been provided to solve the problems faced by the industrialization of optical thin film. It includes high intensity laser, diamond and diamond-like film, soft X-ray multilayer film, solar selective absorption film and optical communication film.


Luminescent film in the field of illumination


Lighting area is now very widely used quartz halogen lamp, it has small volume, high luminous efficiency, light failure is small, the advantages of long service life, high color rendering index, especially made of optical thin film technology "targeted cold reflection halogen tungsten lamp", infrared transmission, due to its source and the advantages of visible light is a directional reflection has been more and more widely used, whether industrial lighting, projection lamp, projection lamp, medical lamp light source, rear projection TV, etc.), commercial lighting, shopping malls, restaurants, jewelry, clothing, etc.), or home lighting (decoration), bright prospect of market.


Is one of the core technology in cold reflection cup coating technology has been an unprecedented success application of the coated visible reflection and transmission of infrared light cup has obvious advancement, with the conversion only one over ten international prices of domestic equipment, the coating technique and technology of Chinese characteristics, make cold light cup has a great advantage, high cost performance in the world, almost all the cold light of lighting giant in the world (light) to buy from China, China's exports in 300 million yuan of above.


The principle and research of cold light film


The design principle of the cold light film is to be able to reflect visible light as high as possible, while the transmitted infrared light, plated on the curved reflective bowl, makes the reflected light very high, and the infrared radiation heat is greatly reduced, thus reducing the temperature of the beam. The illume that makes with this kind of technology shoots the light to be called cold light lamp. Cold light film is actually a kind of wideband reflection film with long wave passageway. It should have certain visible band and good passageway of long wave. The design principle of high reflection film and spectroscopic film can be used as the solution. In order to obtain a wide reflection band in the visible area, two methods can be used:


1. Design high reflection film systems with different center wavelengths and connect their high reflection bands to obtain wide high reflection bands.

2: design the film system whose thickness varies according to geometric or arithmetic progression. The purpose of the design is to form a film system whose central wavelength changes constantly, so as to obtain a wideband high reflective film.


In order to obtain high transmissivity in the infrared region, suitable infrared transparent film materials and through - band matching layer technology can be used. It should be pointed out that the positioning of the width of the reflector band has an important influence on the integrated spectrum, color temperature, illuminance and luminous flux of cold light lamps, and it must be specially designed and controlled as required.


Classification of luminescent films


Because of the choice of coating materials, the characteristics and application range of reflective bowls are different.


Soft film


The coating material is ZnS-MgF2 combination. Its characteristic is to make convenient, craft is mature; Disadvantages of firmness, water resistance, temperature resistance, durability is poor, such as the use of ion-assisted coating technology can improve its characteristics. It is often used in the occasions with low requirements, and is applied to the cold light spotlights with the service life below 1000h.


Half Hard film


The coating material is ZnS-SiO combination. This is of great value to the combination of materials. Some literatures reported that silicon monoxide and zinc sulfide are not suitable for high and low refractive index materials as they are prone to film cracking due to stress mismatch. And now the research has proved that, as a result of the necessary and unique process preparation technology, so this kind of film is very strong, water resistance, temperature resistance is also very ideal, the film can withstand boiling water cooking, the film material production in the cold light spotlights, service life in 2000h above. It has been used as the preferred film material for cold light film, and it can also be recommended for other coating products.


Hard film


The coating material is T io2-sio2 combination. This combination film has good performance indexes, and can be used for cold light film products with harsh conditions, such as reflective bowl of film projector, and cold light spotlights with a service life of 4000h. Its disadvantages include high requirements for equipment, complicated production process and high production cost.


Optical thin film coating technology


The coating technique of optical thin film is to deposit the thin film material into thin film according to certain technical ways and specific requirements. Optical thin film can be used in a physical vapor microscopy deposition (PVD), chemical vapor deposition (CVD) and chemical liquid deposition (CLD) three kinds of technology to the preparation, physical deposition (PVD) in the preparation of optical thin film gas reading this technology has been widely adopted, which makes all kinds of optical thin film has been widely used in various fields, the following coating online introduced the preparation technology.


Physical vapor deposition (PVD)


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Physical vapor deposition is a mainstream technique for the preparation of optical thin films. Physical vapor deposition simply means that the thin film material is heated in a vacuum environment to turn into steam, which then condenses onto the substrate at a relatively low temperature to form a thin film. PVC requires the use of vacuum coating machine, high manufacturing costs, film thickness can be accurately controlled, film strength is good. PVD optical thin film preparation technology has been widely used, so that a variety of optical thin films in various fields have been widely used. In the PVD method, according to the film material vaporization mode, and divided into thermal evaporation, sputtering, ion plating and ion - assisted plating technology. Among them, optical thin films mainly use thermal evaporation and ion-assisted plating technology, sputtering and ion-assisted plating technology for the preparation of optical thin films is developed in recent years.


Chemical vapor deposition (CVD)


Chemical vapor deposition (CVD) generally requires a high deposition temperature, and specific precursor reactants are required before the preparation of thin films. The deposition rate of thin films prepared by CVD technology is generally high. But some by - products, such as flammable and toxic, can also be produced in the film preparation process.


Chemical liquid deposition (CLD)


Chemical liquid deposition (CLD) process is simple, the manufacturing cost is low, but the film thickness can not be accurately controlled, the film strength is poor, it is difficult to obtain multilayer film, but also cause waste water, waste gas pollution.


Application prospect of optical thin film


Photoelectric information industry of the most promising of the communication, display and store the three types of product cannot leave the optical thin film, such as projector, back projection television, digital camera, video camera, DVD, and the DWDM optical communication, the GFF filter, etc., the performance of optical thin film to a great extent, determines the final performance of these products. Optical thin film is break through the traditional category, more and more widely permeates the space probe, integrated circuits, biological chip, laser device, liquid crystal display to the field of integrated optics and so on various subjects, and the progress of science and technology plays an important role in the development of global economy, studying the characteristics of optical thin film physics and technology constitute a branch of modern science and technology, thin film optics. Optical thin film technology has become one of the key technologies to measure the development level of national high-tech industries such as optoelectronic information.


Anti-reflection anti-ar film, mainly to deal with the large wind sand. Like dust, sand, will have an impact on the anti-reflection film scratches. This is the anti-reflection film moisture and cold resistance, friction resistance.