First, the technical background Information transmission in the digital age is so efficient, partly thanks to the rapid development of fiber-optic communication technology. The fiber was originally born as an endoscope for medical use. Due to the limited technology at that time, the transmission attenuation of light in the optical fiber was very large, so researchers at the time were not optimistic about the application of optical fiber in communication. After that, through the painstaking research of the British Chinese Dr. Gao Wei, and put forward bold assumptions, they rekindled the enthusiasm of researchers for optical communication. After several years of research, lasers and low-loss fibers have made major breakthroughs, which made optical communication possible. Optical fiber was originally widely used in the broadcasting industry, while the security industry in the same period still uses coaxial cable as the main transmission medium. However, with the development of digitalization and high definition in the security industry, traditional transmission media can no longer meet the security industry's requirements for transmission bandwidth, transmission rate, transmission distance, and confidentiality. Fiber-optic communication technology has been introduced into the security industry. And it developed quickly. At present, optical transmission is the core technology of video surveillance long-distance transmission solution. As the core of the entire transmission scheme, high-performance optical transceiver equipment has also become the research and development focus of security manufacturers such as Hikvision, and plays a pivotal role in the entire security monitoring system. Second, the classification of optical transceivers According to the different processing methods of the input signal, the optical transceiver can be divided into an analog optical transceiver and a digital optical transceiver. (1) Analog optical transceiver The analog optical transceiver performs PFM modulation on the analog signal, then performs electro-optical conversion, performs optical-to-electrical conversion on the receiving end, and then restores the video signal through PFM demodulation. This method has a high signal-to-noise ratio and a small nonlinear distortion, so that the signal can easily be transmitted for several tens of kilometers, but the number of signal paths transmitted by a single optical fiber is limited. (2) Digital optical transceiver The digital optical transceiver performs analog-to-digital conversion on the input analog signal, so the digital signal is transmitted in the optical fiber, and the digital signal directly controls the strength of the optical head transmitting signal (that is, the signal strength is represented by the number 1, and the signal weak is represented by the number 0). The receiving end performs a number of analog conversions to restore the original video and audio signals. The digital signal has a lower error rate than the analog signal, which can ensure the distortionless reduction of the video signal, and the multi-channel signal can be transmitted without interference in one path of the optical fiber, so that the multiplexing efficiency of one optical fiber is greatly improved. It can realize dozens of roads and even hundreds of road images for one optical fiber transmission. Just as digital replacement of analog in the field of cameras, digital optical transceivers in the world of optical transceivers will also replace analog optical transceivers. This article focuses on digital optical transceivers. The digital optical transceiver is further divided into a digital video optical transceiver and an Ethernet optical transceiver, that is, a network optical transceiver. Digital video optical transceiver The digital video optical transceiver can transmit uncompressed video signals, such as HD-SDI signals, to solve the transmission bandwidth problem in the traditional transmission mode, making it possible to transmit uncompressed high-definition video signals in real time, greatly improving the picture quality in real-time monitoring. A certain type of digital video optical transceiver can transmit 485 control signals, audio signals, etc. while transmitting video signals. According to different application scenarios, digital video optical transceivers can be divided into point-to-point optical transceivers, node optical transceivers, convergent optical transceivers, coarse wavelength division multiplexing optical transceivers, and integrated service video optical transceivers. (1) Point-to-point optical transceiver A fiber can only have one transmitting end and one receiving end, and the transmitting end and the receiving end appear in pairs (see Figure 1). Therefore, several senders need several fibers, and they can only form a star network. Each monitoring point is independently transmitted by its own fiber line. If the number of input terminals is large, it is easy to cause waste of the fiber, which is not conducive to laying lines on the project. Cable and control of cost. Figure 1 point-to-point optical transceiver connection diagram (2) Node type optical transceiver Each node type optical transceiver is finally connected to the center receiving end through series connection, mainly using signal multiplexing technology, the optical signal is multiplexed once every node, and the signal of the node is multiplexed into the previous signal and transmitted to Next node (Figure 2). Therefore, multiple nodes can exist on one fiber line, which greatly saves the cost of laying the fiber. This type of optical transceiver is widely used in highway projects. Figure 2 node type optical transceiver connection diagram (3) Convergent optical transceiver The front-end multi-path fiber signals are transmitted to a convergence node through their respective transmitting optical transceivers. The optical transceivers of the aggregation node combine the multiple optical fiber signals into one optical signal and transmit it to the central convergence receiving optical transceiver (see Figure 3). Such a transmission method can convert a traditional star topology into a tree topology, which greatly saves the cost of fiber laying and increases the flexibility of the entire network. Figure 3 Convergence optical transceiver connection diagram (4) Coarse wavelength division multiplexing optical transceiver The coarse wavelength division multiplexing optical transceiver uses an optical multiplexer to multiplex optical signals of different wavelengths into a single optical fiber for transmission, and at the receiving end of the link, the mixed signal in the optical fiber is decomposed into signals of different wavelengths by means of an optical demultiplexer. , connected to the corresponding receiving device (Figure 4). The spacing between the wavelengths in the coarse wavelength division multiplexing system is wide, so the accuracy of the laser transmitter is low, and the cost of the entire transmission system can be saved. Figure 4 The working principle of the coarse wavelength division multiplexing optical transceiver (6) Integrated business optical transceiver The integrated service optical transceiver combines digital uncompressed technology with TDM and WDM technologies to simultaneously transmit video signals, Ethernet signals, telephone signals, voice intercom, bidirectional data, and switching information using a single fiber (see Figure 5). Because in large projects and complex applications, simply transmitting video signals can no longer meet the growing security surveillance needs. For example, if the front end is an analog dome camera, if only the video signal is transmitted, the control of the dome camera cannot be realized. Therefore, the 485 control signal is transmitted while transmitting the video signal to achieve low-latency control of the dome camera. Under such demand, the integrated business optical transceiver came into being, meeting the needs of large-scale networking of the entire system. Figure 5 Integrated service optical transceiver topology 2. Network optical transceiver The network optical transceiver can convert the electrical signals in the twisted pair into optical signals for long-distance transmission, and can also be used through fiber cascading and group ring. It is mostly used for network construction in projects such as factories, transportation, rails, mines, and power stations. Third, the important parameters of optical transceivers and product selection (1) Data type The signals transmitted in a large-scale integrated project are very diverse. Before purchasing an optical transceiver, you must first know what type of signal source is input at the front end. Depending on the type of input source, such as analog signal, network signal, and HD raw data, select different types. The optical transceiver performs matching. (2) Fiber type The optical transceiver is divided into single fiber transmission and dual fiber transmission. When transmitting with a single fiber, the transmitted and received signals are transmitted in different wavelengths in one fiber without mutual interference. When transmitting with dual fibers, both the receiving and transmitting are transmitted using a separate optical fiber, and the wavelengths of the two can be the same. When using single-fiber transmission, since two wavelengths of signals need to be multiplexed in one light, a pair of wavelength division multiplexers are transmitted in each optical transceiver than dual-fiber transmission, and dual-fiber transmission is more used than single-fiber transmission. An optical fiber. Optical fibers can be classified into single-mode fibers and multimode fibers according to different transmission modes. Single-mode fibers have a longer transmission distance but are also more expensive than multimode fibers. Before designing the solution, it is necessary to fully consider the actual needs and then select the corresponding optical transceiver and optical fiber. (three) wavelength The transmitting wavelength of the transmitting end of the optical transceiver needs to match the receiving wavelength of the receiving end. For example, Tx1310nm/Rx1550 vs. Tx1550nm/Rx1310. (four) transmission rate The transmission rate of the optical transceiver at the transmitting end needs to match the rate of the receiving end. (5) Transmission distance According to the different transmission distances, the optical transceivers will have different price. In actual projects, please select the suitable optical transceiver products according to the transmission distance. The common transmission distance is 10 km, 20 km and 40 km. Conclusion With the implementation of large-scale security monitoring projects and the demand for ultra-high-definition video surveillance, optical fiber transmission will become a video surveillance transmission network with its characteristics of good confidentiality, light weight, strong anti-interference ability, long distance and high data bandwidth. The core technology is widely used in telecommunications, electric power, public security, military, highway transportation, railway, customs, large factories and mines, government agencies and other projects. 2Pans Buffet Server,Buffet Server Warming Plate,Buffet Server Warmer,2Pans Buffet Server Warmer Shaoxing Haoda Electrical Appliance Co.,Ltd , https://www.hotplates.nl
