In order to avoid Nichia's blue LED plus fluorescent powder technology patents, various industries have invested in other LED technologies that can emit white light. The most anticipated technology is to use UV LEDs to achieve white light, but UV LEDs still have two difficulties that are difficult to overcome, such as light leakage and low brightness. In addition to continuing efforts to solve related problems, it is necessary to seek other materials or technologies to achieve LED technology that emits white light.
In 1987, two scholars with different nationalities and different locations, Eli Yablonovitch and Sajeev John theoretically found that the propagation state of electromagnetic waves in periodic dielectrics has a band structure, using two or more different refractions. The rate (or dielectric constant) material is periodically changed to achieve the photon energy band. Therefore, Photonic Crystal (PhotonicCrystal) has been discovered for nearly 20 years, and its application in various fields has a very impressive performance. It has always been a technology that developers are concerned about.
At present, the use of two-dimensional photonic crystals to achieve the technology of white LEDs has been gradually developed, making the future Photonic Crystal LEDs become the focus of attention and the expectation of getting rid of the Nichia patents.
1. Photonic crystal characteristics and structure
Photonic crystals appear in a periodic structure with different wavelengths, and photonic crystals of primary, secondary and cubic elements can be developed separately. Among these structures, the most famous one is the three-dimensional photonic crystal structure. However, the three-dimensional photonic crystal is very difficult to manufacture and commercialize. The reason is that the main research field is still the photonic crystals that are retained in the second element. Therefore, the photonic crystal LEDs developed by various industry players in the LED field today are also two-dimensional photonic crystals.
The general material construction is a fixed structure, so the material itself will have a certain refractive index. Wave Number and frequency have an effect on the refractive index of a general material. The horizontal axis is the wave number of the substance, the vertical axis is the frequency, and the oblique line represents the refractive index. The refractive index is a very proportional growth, which means that no matter what wave number or wavelength, its refractive index is constant. Then what kind of structure is the photonic crystal, and then from another angle. The characteristic of a photonic crystal is the periodic structure, which results in multiple reflections.
The ratio of the number of wavenumber vectors formed by the photonic crystal to the frequency ratio of the light, the curve of the frequency is not so simple, and the curve has become very complicated. This curve changes with the directionality of the light, that is, the anisotropy, and Its polarizing properties can be used to design different products. Photonic crystals have a well-known feature. I believe everyone knows that it has a light gap. In this area of ​​the optical energy gap, light does not exist. The curve here is also the same as the slope of Figure A, which is the opposite of the refractive index. As long as it is at this point, the slope is equal to zero. So outside of this point, the speed of light does not produce zero. So it can also be said that the photonic crystal can also control the speed of light.
To put it simply, the purpose of using photonic crystals is to condense into one sentence, which is to use artificial structures to control this optical property.
2. Differences between photonic crystals and solid-state light-emitting elements
Photonic crystals have three optical properties that can be controlled manually for different purposes. The first characteristic is that if the optical energy gap is used, the light can be blocked. This feature allows you to lock the light in a fairly small area. In the industry today, this feature is used to concentrate light in an area and make it into an integrated circuit.
Another characteristic is that the photonic crystal has an anisotropy, and the photonic crystal's light will scatter in many directions because the photonic crystal can appear to be transparent and opaque with the polarization angle of the light. But there are some ways to pass through).
The third characteristic is that the curve of the photonic crystal is very complicated and varied. Because the curve of the photonic crystal changes very quickly and is very irregular, as long as the wavelength changes slightly, the light entering the photonic crystal can be seen, and its angle will deviate very much. In terms of advantages, the area of ​​photonic crystals is one thousandth smaller than that of conventional integrated circuits, so the cumulative degree of circuits is increased by 1,000 times compared with the past. Another advantage is that the foldability multiple can be up to 1,000 times the previous one.
In addition, it is also possible to use a polarizing property to change the properties of light, and it is possible to condense the polarized light of the conventional square into one thousandth of the conventional volume. In short, what are the benefits and characteristics of photonic crystals? High accumulation, small size and low cost.
3. Using LED photonic crystals to make LEDs
In addition, photonic crystals have other properties. With its characteristics, photonic crystal LEDs can be fabricated. Generally, it can be divided into two types, one is an LED, and the other is a laser diode (Laser Diode). LD laser diode part can be divided into photonic crystal DFB laser diode (Photonic crystal DFB LD) and Photonic crystal defect LD. Photonic crystal DFB laser diodes are well-known structures. Their laser values ​​can be controlled in very low areas for emission. The structure of such a sub-structure is the area where the optical energy gap must exist. Because of this, this structure It is more difficult to achieve commercialization.
It is relatively simple to make LEDs by using the structure of photonic crystals. The part that is often confused about photonic crystals is that they use DFB lasers, so some people think that they are using a specific period or wavelength. In fact, the answer is wrong. The reason is that the DFB laser and the photonic crystal LD ​​have limited incidence of incident and diffracted light. However, the incident light angle and the diffracted light angle with respect to the photonic crystal are not limited. So instead of using specific cycles or wavelengths to enhance efficiency, this feature is very important for LEDs.
The various TELEPERM M automation systems have different designs, ranges of functions and performances. The AS 235, AS 235 H and AS 235 K automation systems described in this catalog are proven and reliable. They can be configured within wide limits and coupled to a wide range of subordinate systems. The AS 235 H additionally has a redundant central unit and thus satisfies particularly high availability demands. The AS 235 systems can communicate with one another and with higher-level systems via the TELEPERM M CS 275 plant bus. A wide range of TELEPERM M input/output modules is available for connection of the process peripherals (sensors and final control elements) to the AS 235, AS 235 H and AS 235 K automation systems. Some modules have their own processing features or can be configured application-specific. The AS 388/TM and AS 488/TM automation systems (see Catalog PLT 112) use the SIMATIC M7-300 and M7-400 automation computers as the hardware platform and are compatible with the AS 235 system. They are appropriate for the extension of existing TELEPERM M systems or for the design of new systems. The AS 388/TM and AS 488/TM systems can be operated on the PROFIBUS-TM plant bus. PROFIBUS-TM is based on the standardized PROFIBUS. The AS 488/TM system can additionally be operated on the CS 275 plant bus. ET 200M distributed I/O systems with a comprehensive range of I/O Modules can be connected to the AS 388/TM and AS 488/TM systems via one or two PROFIBUS-DP interfaces.
Siemens Teleperm Programmable Controller
Siemens Teleperm Programmable Controller
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