■ Importance of optical film and coating technology
From precision and optical equipment, display equipment to optical film applications in daily life; For example, glasses, digital cameras, various household appliances, or anti-counterfeiting technology on banknotes can all be called an extension of the application of optical film technology. Without optical thin film technology as the basis of development, the development speed of modern photoelectric, communication or laser technology will not progress, which also shows the importance of optical thin film technology research and development.
Generally speaking, when using multilayer films, we must design various types of optical films by using high and low refractive index film stacking technology according to the needs of designers, so as to achieve the optical characteristics expected in advance and evaluated afterwards. For example: anti-reflector, high reflector, beam splitter, cut-off filter, band-pass filter, band-stop filter, etc. Today, with the development of computer analysis software and hardware, not only the design of optical thin films becomes more convenient, but also the research and development of optical thin film technology will be faster.
As far as the current design end is concerned, if the reasonable range of characteristics is considered, the threshold for making optical films has been reduced a lot, and technical difficulties rarely appear. In general, it is not difficult for designers to publish suitable optical multilayer film structures as long as they are within reasonable requirements. However, the most important key problem of optical thin films lies in the improvement of thin film coating technology? This is related to how to accurately control the thickness and refractive index of each film to obtain the expected optical and mechanical properties, even in the process of mass production and cost reduction. In addition, the development of thin film materials (including material testing, chemical purity, material innovation and material types), the development of advanced coating technology (including vacuum coater and monitoring technology) and the measurement and analysis of thin films (thin film design and thickness error analysis skills) are the primary topics to be faced by optical thin film engineering.
However, in the application of optical thin film technology, because the technology itself is summarized as a wide range of applications, it is not easy to distinguish a product or a single product as a carrier; Therefore, in the optical film product technology, the final application is on many optical elements. If we explore the relevant application market of optical components, we can see the main added value and correlation.
■ Application of optical thin film technology in display industry
The requirements for display screen size, image quality and radiation are more and more strict. In the past, the size of the display also changed from 14 inch, 20 inch, 29 inch, 32 inch, or even larger, and it also developed from CRT screen to LCD screen or projection screen. Because CRT monitors over 40 inches 100 kg and the thickness is over 35 inches; Therefore, in the general CRT display production process, more than 40 inches is the technical bottleneck. At present, the technology to break the size bottleneck is to use projection technology to enlarge the size of the display through optical technology, so that its body thickness becomes thinner and its volume becomes lighter.
▲ For the projector industry, it is necessary to quickly meet the requirements of light source progress, higher brightness, contrast, smaller size and lighter weight. (photo by Luo Qingyue)
Uncovering important optical key components in projection display technology, such as optical engine, light valve, polarization converter and other development technologies, has a key impact on the image quality in projection display technology. For example, the polarizing beam splitter prism in the optical engine is an indispensable optical element in the optical engine, and its visible light wave is required to be at 420? Only in the range of 680nm (about 30 incident angle) can P polarized light and S polarized light be separated greatly, and the P polarized light transmittance Tp > 90% and extinction ratio TP/TS > 500 can be maintained. This is because the higher the extinction ratio, the higher the TP transmittance, the better the image contrast, the higher the color consistency and the higher the light energy utilization rate.
A large number of polarization, light splitting and filtering components are used in the optical engine, which need to be realized by optical thin film and coating technology. However, the coating technology of these components is very demanding, which leads to increased production difficulty. Generally speaking, projector technology is developed at present, including LCD, DLP(MEMS) and LCOS. Imaging technologies are divided into transmissive LCD, reflective DLP and LCOS. In the projector system, it is necessary to use the newly developed optical thin film filter technology to achieve the best image quality.
For the projector industry, in order to meet the requirements of light source technology, higher brightness, contrast, smaller size and lighter weight, all kinds of optical components used in it must have corresponding solutions. In order to meet the demand, the traditional integer stack design can no longer be used in optical thin film technology, and non-integer stack design should be widely used if necessary. However, for non-integer film stack technology, besides the inherent difficulties in design, it is also quite difficult in practical plating. On the other hand, the requirements of environmental testing are stricter, the selection of filter materials should be more cautious, and the stress behavior of the whole filter should also be considered in the selection of substrate ... and so on, which must be considered at the beginning of the preliminary design.
■ Optical thin film technology is also helpful for nanotechnology.
With the development of science and technology, people pay more and more attention to nano-materials and technology. The main reason is the wide application of nano-materials and future considerations. On the one hand, the existing theoretical basis does not cover the complete development of nano-materials; On the other hand, the impact and integration from physics, chemistry, biomedicine and other fields have provided extremely powerful help. Among them, the physical aspects focus on nano-manufacturing, material detection technology and atomic manipulation; In chemistry, it provides a small and broad, bottom-up assembly method and various chemical methods to synthesize nanomaterials; The biological field mainly provides bionic concepts and nano-material synthesis technology for bio-manufacturing engineering.
Looking back on the development of optical thin film technology, the past optical thin film technology has entered a mature stage and has been widely used. Some experts also pointed out that after five years, the micron-scale electronic circuit technology with "silicon" as the main material will probably face the end of development. However, due to the progress of manufacturing technology in recent years, the characteristics of nano-scale optical films are gradually discussed by the industry. This is because once photonic components want to echo electronic circuits on smaller, faster and lower energy lines, the manipulation of photons must be hundreds of times smaller in space, speed and energy than it is now. Therefore, nano-photonic waveguide may become the best material to replace some silicon and other semiconductor materials, and it can effectively develop transmission speed and density as high as 50? /kloc-more than 0/00 times; In addition, the energy saving benefit is 50? 100 communication and operation device. Therefore, the research of optical thin film technology will become a very important key factor under the impetus of nano-size.
At present, most optical components that can be manufactured by integrated optical technology are electro-optic, acousto-optic modulator, optical splitter, splitter/demultiplexer, etc. If we want to realize all-optical or multi-component integrated optical elements, we must have "nano-optical thin film elements". Among them, the most concerned thing is that photonic crystals formed by combining thin film technology and lithography technology have periodic dielectric distribution structure characteristics, thus improving the resolution and making smaller feature sizes, so that there are more transistors in the same unit area and the density is higher.
Generally speaking, photonic crystals can be divided into two categories according to the directional characteristics of photonic bands, that is, signal transmission is unidirectional and omnidirectional; Unidirectional photonic band can only suppress the propagation characteristics of light waves in a certain propagation direction, while omnidirectional photonic band can suppress the propagation characteristics of optical modes in all propagation directions. Therefore, light can be reflected by the structural design, resulting in zero energy penetration. Except for photonic crystals, when the optical thin film is made of nano-scale periodic holes on the metal thin film, when the wavelength of the incident light is longer than the period of the holes, the incident zero-order light has extremely high transmittance and will not be diffracted. This kind of optical element mainly uses the surface plasmon characteristics of metal to produce characteristics completely different from the traditional optical theory, which will be different from a new type of state and surface plasmon element under the characteristics of photonic crystals.
The above two different types of devices, whether photonic crystals or surface plasmon devices, need nano-scale precision lithography, etching technology and optical thin film technology. Therefore, if we take optical thin film technology as the main development foundation, plus lithography technology and thin film characteristic analysis technology, the ultimate goal can be to fully understand the analytical characteristics and composition structure of optical thin films on the nanometer scale, so as to provide the development and application of nano-optical thin film technology in the field of integrated optics.
▲ The Film Technology Center established by Central University demonstrated the application technology of a number of film products. Film applications can be seen everywhere, and all kinds of films have their functions. (photo by Luo Qingyue)
■ Not a major star industry, but its importance cannot be ignored.
It can be said that "optical thin film technology is not a brilliant technology". However, ... is an indispensable part of industrial development in Taiwan Province Province, which not only affects the quality of products, but also affects their efficiency. Optical thin film technology gives people the feeling of being "transparent" and "thin", but the knowledge inside can not be summarized by words alone. Although the application of optical thin films mostly belongs to green leaf technology, it is only an auxiliary function. Once the optical thin film technology comes out, it will not only make the function of the product more obvious, but also enhance its added value.
Just like ordinary glasses, the application of optical coating technology can reduce the reflectivity of glasses and make them have higher penetration, while anti-ultraviolet lenses and anti-infrared lenses are also applications of optical coating technology. In optical communication, display, lighting, energy saving and so on. Optical thin film technology can also be applied. For example, the research and application of cutting-edge technology foundation requires smaller and more exquisite components to make products lighter and shorter. In other words, as long as it is applied to optical components, optical films can be used to improve their quality and technology, making products more perfect and closely related to life.
Although the technology and theory of optical thin film have a long history, with the rapid improvement and growth of related scientific and technological environment, how to innovate optical thin film technology will still be the goal that people engaged in optical thin film technology need to pursue. At present, Taiwan Province manufacturers focus on the following stages: OEM technology and plastic packaging manufacturers, but in terms of optical quality and reliability, they must continue to improve. As for the optical coating technology above OEM level, for example, although some manufacturers have invested in research and development, mass production is still difficult to achieve. Therefore, once Taiwan Province manufacturers can invest heavily in developing new optical thin film technology as soon as possible, it will be helpful to gain important opportunities in the overall optical component market and establish a complete optical industrial structure foundation.
References:
Li Zhengzhong's thin film optics and coating technology, Central University's research center for thin film technology, J. Mort and F. Jansen's thin film deposition and thin film technology.
▲ Dr. Li Zhengzhong said that at present, various photoelectric equipment and optical instruments are related to optical thin film technology; Examples include optical fiber communication, biochip, optical display, satellite, space telemetry system, semiconductor laser, MEMS, optical information storage and various optical elements. (photo by Luo Qingyue)