HIFU Piezoelectric Ceramic Parts
High Intensity Focused Ultrasound (HIFU) technology is to focus ultrasound on a single point to produce high energy, function on the dermis and SMAS layer of skin, stimulate the proliferation and recombination of collagen, effectively achieve the effect of compact contour and smoothing lines.
Focused ultrasound does not heat the skin surface, nor does it need to pass through the skin as a medium for the transmission of laser energy, so it does not affect the tissue on the skin surface and the tissue through which the laser passes, of course, there will be no excessive heat residue on the skin surface. In this way, the epidermis will not be affected by heat, which can reduce the Eastern people's thermal reaction easily, and greatly reduce the chance of scald. Focused ultrasoundtherapy produces thermal coagulation points in the SMAS layer, and the thermal effect diffuses outward from the coagulation points, so the heat source is concentrated in the SMAS layer to be treated. It can produce more collagen denaturation.
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1.2 Single-mode fiber Single-mode fiber refers to an optical fiber that transmits only one light-conducting mode (fundamental mode). Its main advantages are small attenuation, long transmission distance and large transmission capacity, which are widely used in long-distance backbone network, metropolitan area network, access network and other occasions. Single-mode fiber can only transmit the fundamental mode, there is no delay difference between modes, and it has a much larger bandwidth than multimode fiber. The bandwidth of single-mode fiber can reach more than tens of GHz. Therefore, single-mode fiber is particularly suitable for long-distance, large-capacity communication systems. With the continuous development of optical fiber manufacturing technology and communication technology, the types of single-mode optical fiber are also developing.
Commonly used single-mode fibers are as follows:
1.2.1 G.652 fiber G.652 fiber is a conventional fiber, which has two windows of 1310 nm and 1550 nm. The zero dispersion point is in the 1310nm window, and the minimum attenuation is in the 1550nm window. Typical values ​​of these two windows are: 1310nm window attenuation is 0.3 ～ 0.4dB / km, dispersion coefficient is 0 ～ 3.5ps / (nm.km), 1550nm window attenuation is 0.19 ～ 0.25 dB / km, dispersion coefficient 15 ～ 20ps / (nm.km).
1.2.2 G.653 fiber G.653 fiber is dispersion-shifted fiber, also known as 1550nm window performance fiber. By designing the fiber refraction profile, the zero dispersion point is moved to the 1550nm window to match the minimum attenuation window of the fiber, so that the 1550nm window has both minimum dispersion and minimum attenuation. Its typical value in the 1550nm window is: the attenuation coefficient is 0.19 ～ 0.25dB / km, the zero dispersion point is in the wavelength region of 1525 ～ 1575nm, and the dispersion coefficient in this interval is <3.5ps / (nm.km). The good characteristics of this fiber in the 1550nm window make it the best choice for single wavelength, large capacity, and ultra long distance transmission. If the system expansion is carried out purely along the time division multiplexing TDM method, the 20Gbit / s system can be opened directly without any dispersion compensation measures. The important drawback of G.653 fiber is that the four-wave mixing phenomenon limits the use of wavelength division multiplexing (WDM). The so-called four-wave mixing phenomenon is caused by the nonlinearity of the optical fiber. When different wavelengths are simultaneously transmitted in one fiber, new sum and difference wave components will be generated due to interaction.
1.2.3 G.655 fiber G.655 fiber is a non-zero dispersion-shifted fiber. It is to solve the serious four-wave mixing effect in G.653 fiber. The zero dispersion point of G.653 fiber is moved to make 1540 The dispersion coefficient in the range of ~ 1565nm is maintained at 1.0 ~ 4.0 ps / (nm.km), avoiding the zero dispersion region and maintaining a minimum dispersion value, so that it is easier to open a multi-wavelength WDM system. In the characteristics of G.655 fiber, except for the zero dispersion point, other characteristics are the same as G.653. It has the smallest attenuation coefficient and dispersion coefficient in the 1550nm window. Although its dispersion coefficient value is slightly larger than that of G.653 fiber, compared with G.652 fiber, it has greatly alleviated the dispersion-limited distance. It successfully solves the shortcomings of the dispersion limitation of G.652 fiber in the 1550nm wavelength region and the difficulty of wavelength division multiplexing of G.653 fiber, and has the advantages of these two fibers. It can not only open high-speed 10Gbit / s and 20Gbit / s TDM systems, but also expand capacity in WDM mode.
2 Ways to increase optical fiber transmission capacity In theory, there are several ways to increase optical fiber transmission capacity: space division multiplexing (SDM), electrical time division multiplexing (TDM), wavelength division multiplexing (WDM), optical frequency Division Multiplexing (O FDM), Optical Time Division Multiplexing (O TDM) and Optical Soliton Technology (Soliton). Based on practicality, only two expansion methods of TDM and WDM are briefly introduced.
2.1 Time-division multiplexing technology (TDM) TDM technology is a technology for time-division multiplexing signals and is a traditional way of capacity expansion. 34, 140, 565 Mbit / s of PDH and 155, 622, 2488, 9952 Mbit / s of SDH are multiplexed on electrical signals. According to statistics, below 215Gbit / s, the transmission price per bit of the system can be reduced by about 30% for each upgrade. Because of this, in the past upgrades, people first adopted the TDM technology. With the increase of multiplexing rate, for example, when it reaches 10Gbit / s, it is close to the limits of silicon and arsenic technology. There is not much potential to be tapped. The impact of fiber dispersion is also more serious, and higher requirements should be placed on the fiber. 2.2 Wavelength division multiplexing technology (WDM) The so-called wavelength division multiplexing technology is to make full use of the huge bandwidth resources (about 25THz) in the low-loss region of single-mode fiber, using a wavelength division multiplexer (wave combiner) to send At the end, the signal optical carriers of different specified wavelengths are combined and sent into an optical fiber for transmission. At the receiving end, a wavelength division multiplexer (demultiplexer) separates these optical carriers carrying different signals at different wavelengths.
The main characteristics of the wavelength division multiplexing technology are: ①Can make full use of the huge bandwidth resources of the optical fiber, so that the transmission capacity of an optical fiber is increased several times to tens of times than the single wavelength transmission. ② Make N wavelengths multiplexed and transmitted in single-mode optical fiber, which can save a lot of optical fiber in large-capacity long-distance transmission. ③Because the signal wavelengths transmitted in the same optical fiber are independent of each other, they can transmit signals with completely different characteristics to complete the integration and separation of various business signals, including digital signals and analog signals, and the integration and separation of PDH signals and SDH signals. ④ The wavelength division multiplexing channel is transparent to the data format, that is, it has nothing to do with the signal rate and electrical modulation mode, and is an ideal means for network expansion and development. ⑤Using WDM technology to select routes to achieve network exchange and recovery, which may realize the future transparent and highly survivable optical network.
3 Suggestions on the correct selection of optical fiber Three key parameters must be considered when choosing the type of optical fiber: â‘ Maximum non-relay transmission distance â‘¡ Maximum bit rate per wavelength â‘¢ Number of wavelengths per fiber. Of course, the above parameters should consider the requirements of the end of the fiber, rather than the initial requirements. According to the above parameters, if the maximum non-relay transmission distance is 50-100km (depending on the type of laser), then G.652 conventional fiber is a more suitable choice because of its low price. If the distance is longer, and the maximum bit rate of each wavelength is less than 10Gbit / s, then conventional fiber should be preferred. If the distance is long, but only a single wavelength high rate (above 10Gbit / s), then G.653 dispersion can be used. Displace the fiber. If the distance is long and multiple wavelengths need to carry 10 Gbit / s or higher, then G.655 non-zero dispersion-shifted fiber is the best choice.
Therefore, the following principles of fiber selection can be proposed: â‘ Short-distance trunk optical cables and access network optical cables have short distances, and the increased investment of using more fiber cores is not large. Therefore, G.652 conventional optical fibers should generally be selected. â‘¡Long-distance optical cable has a long transmission distance, and the investment increases when more fiber cores are used. Therefore, high-speed and multi-wavelength wavelength division multiplexing technology must be used, and G.655 dispersion-shifted fiber should be given priority.
According to reports, in recent years, North America is setting off a new wave of fiber laying, but G.652 fiber has been stopped on the main line, but G.655 non-zero dispersion-shifted fiber has been used. This trend deserves attention.
Regardless of whether G.652 fiber or G.655 fiber is used, in addition to the requirements for the conventional indicators such as attenuation and dispersion of the fiber, generally the PMD indicators can be requested according to the transmission rate of 10Gbit / s, so that the wavelength division can be used in the future. The multiplexing method creates the conditions for rapidly expanding the capacity of the transmission system.
Choice 1 Types of optical fiber 1.1 Multimode fiber Multimode fiber refers to an optical fiber that can transmit multiple light conduction modes. In the early stage of optical fiber communication, the multimode fiber (G.651 fiber) was used. Its operating wavelength was 850nm or 1300nm, attenuation constants were <4dB / km and <3dB / km, and dispersion coefficients were <120ps / (nm .km) and <6ps / (nm.km). Because of its large attenuation and dispersion, it can only be used for short-distance communication. However, it has a large core diameter and low requirements for connectors and connectors. It is more convenient to use than single-mode optical fiber and is currently used in computer local area networks.