I. Overview of optical transceiver development As we all know, the introduction of video optical transceivers from abroad to imitate manufacturing, to independent creation of completely independent intellectual property rights, has experienced a transition from analog to digital technology, achieving a leap from single-function to multi-service integrated transmission, from small to large scale use. Application, video optical transceiver with the development of the monitoring industry step by step to maturity.
Since 2001, with the rapid development of broadband digital optical transmission device technology and digital video technology, digital video optical transceivers have begun to move towards the market and gradually replaced the analog optical transceiver market, ushered in the era of rapid development of digital video optical transceivers, and presented the technology Mature, superior performance, wide application, and strong demand.
In recent years, as the demand of the security market has changed, the technical innovations and product changes of video optical transceivers have shown stronger application: (1) In order to meet the needs of highway field monitoring, cascaded link optical transceivers replace traditional ones. Point-to-point optical transceivers are used in large numbers; (2) In order to meet the application of the public security level 3 and 4 networking, multi-function optical transceivers for single-fiber transmission of two-way video, audio, data, telephone, E1, and Ethernet have emerged; (3) With the continuous expansion of the construction scale of Pingan City and the shortage of optical fiber resources, the optical transceiver manufacturers have also launched the convergence of optical transceivers in a timely manner.
At present, security video optical transceivers are showing rapid development momentum, their applications have also increased substantially, core coding and decoding technologies and key technologies have greatly improved and innovated, and practical bottlenecks and problems in application have been greatly improved. This article focuses on the analysis and discussion of the codec technology, technology innovation and application of video optical transceivers.
Second, optical transceiver principle and coding
The optical transmission system consists of three parts: a light source (optical transmitter), a transmission medium, and a detector (optical receiver). The work of the light source and the detector is performed by the optical transceiver. The Optical Multiplexer is a device that transforms multiple E1s (a type of data transmission standard for trunk lines, typically at 2.048 MbPS, which is used in China and Europe) into optical signals and transmits them (its role is mainly to realize electro-optical and optical - Electric conversion). Optical transceivers mainly include analog optical transceivers and digital optical transceivers:
1, analog optical transceiver
The analog optical transceiver adopts the PFM modulation technology to transmit the image signal in real time, which is currently used more often. The transmitting end will first perform the PFM modulation of the analog video signal (generally, there are several methods of frequency modulation, phase modulation and amplitude modulation, so that the analog optical transceiver is divided into several optical transceivers such as frequency modulation, phase modulation and amplitude modulation), and then the electro-optical conversion is performed. After transmitting to the receiver, the optical-electrical conversion is performed, and then PFM demodulation is performed to recover the video signal. Due to the adoption of PFM modulation technology, the transmission distance can easily reach about 30Km, and the transmission distance of some products can reach 60Km or even hundreds of kilometers. Moreover, the distortion of the image signal after transmission is very small, with high signal-to-noise ratio and little nonlinear distortion. By using wavelength division multiplexing technology, it is also possible to realize bidirectional transmission of image and data signals on one optical fiber.
2, digital optical transceiver
Since digital technology has obvious advantages in many respects compared with traditional analog technologies, just as digital technology has replaced analog technology in many fields, the digitalization of optical transceivers is also an inevitable trend. At present, digital image optical transceivers mainly have two technical methods: one is an MPEGII image compression digital optical transceiver, and the other is a non-compressed digital image optical transceiver.
Image compression digital optical transceivers generally use MPEG II image compression technology, which can compress moving images into N×2 Mbps data streams and transmit them over standard telecommunication interfaces or directly over optical fibers. Due to the use of image compression technology, it can greatly reduce the signal transmission bandwidth to facilitate the use of less resources to transmit image signals. At the same time, due to the adoption of the N×2Mbps standard interface, it is possible to use the rich channels of existing telecommunication transmission equipment to transmit monitoring images, which brings convenience to engineering applications. However, image compression digital optical transceivers also have their inherent disadvantages. Its fatal weakness is that it cannot guarantee the real-time performance of image transmission. Because image compression and decompression require a certain amount of time, a delay of 1-2 seconds is generally generated for the transmitted image. Therefore, this kind of equipment is only suitable for places with low requirement for real-time performance. In addition, the image will produce some distortion after compression, and the price of this optical transceiver is also high.
The principle of the uncompressed digital image optical transceiver is to carry out A/D conversion of the analog video signal and multiplex the signal of voice, audio, data, etc., and then transmit it through the optical fiber. It uses a higher data rate to guarantee the transmission quality and real-time performance of the video signal. Due to the very large bandwidth of the optical fiber, this high data rate does not impose excessive requirements on the transmission channel. The uncompressed digital image optical transceiver provides excellent image transmission quality (signal-to-noise ratio is greater than 60dB, differential phase distortion is less than 2, differential gain distortion is less than 2%), achieves broadcast-grade transmission quality, and image transmission is fully real-time. Due to the adoption of digital technology, sophisticated communication technologies such as multiplexing and optical transceiver technologies can be used in the device to improve the reliability of the device and reduce costs.
Third, the existence of optical transceiver problems and technological innovation
The bottleneck encountered by current optical transceivers is how to better integrate into networked applications. Therefore, providing comprehensive and systematic application solutions and improving products and technologies for specific applications is undoubtedly the best solution.
1, optical fiber digital video network management platform
The fiber digital video network management platform (VAM) combines the features of standardization and generalization of Ethernet, the high-quality quality of non-compressed video, and the convenience of application of compressed video, including transmission, exchange, storage, analysis, and processing. Applications and other functions in one, to provide users with a complete video surveillance application system solutions.
The VAM system has many unique advantages: (1) The system encapsulates both uncompressed video and compressed video into Ethernet data packets, and the Ethernet interface is currently the most widely used form of communication interface, so long as it can carry Ethernet transmissions. Both the switched and the system can be used as the transmission and switching channels of the VAM system. (2) The content transmitted and exchanged in the VAM system is uncompressed digital video. That is to say, the VAM system can provide high-quality images to ensure that the surveillance system has no distortion and full real-time requirements on the video. Compressed video can also be transmitted at the same time as non-compressed video in the VAM system, breaking through the concept of traditional video optical transceivers. The VAM system can provide 4 kinds of code streams according to the user's needs and needs a large-screen display place. The VAM system can provide 128M uncompressed video code guarantee, and the general monitor shows that the VAM system can provide the SM with guaranteed clarity and real-time performance. Streaming digital video, desktop browsing can provide 2M compressed video stream, and storage can provide 512K or 2M stream compressed video, while satisfying various needs while having considerable flexibility. (3) In terms of the digitization of video signals, the VAM system complies with international standards ITUBT601, BT656 for digitizing analog video, and BT656 digital video is a standard digital video code stream for compression encoding or video analysis processing. Therefore, in the digitalization process, The VAM system can provide the application system with a video source that minimizes distortion.
2. VPON passive optical network non-compressed digital video
The VPON passive optical network uncompressed digital video optical transceiver is also a system-level product. It creatively applies the PON technology to the transmission of uncompressed video, which brings the benefits of not only saving fiber resources, but also brings great flexibility to the transmission network of uncompressed video. One OLT can access 8 ONUs, and each ONU can access 1 to 3 uncompressed digital videos. The 8 ONUs and OLTs can be connected to any network, chain, tree, or star to apply. Bring great flexibility.
To sum up, standardization and openness can achieve interconnection and interoperability with other devices, and can provide specialized application products. Among them, video encoding technology plays an important role here. For example, a video optical transceiver transmits video signals via an Ethernet interface, a digital video code stream adopts the BT656 standard, and compression encoding employs H. 264 video compression standards, etc., to a large extent ensure the standardization and openness of the system.
Fourth, the application of optical transceivers in the field of video surveillance
Due to the various advantages of optical fiber transmission, the applications of optical transceivers are very extensive. At present, the most widely used aspect of optical transceivers is the transmission of long-distance video and data. In the surveillance areas such as highways, banks, electric power, and telecommunications, the transmission of video signals is required. It is the use of optical transceivers to convert video signals into digital signals through optical fibers. It has a wide application prospect in many fields such as remote video conferencing, distance learning, telemedicine, and communications.
Among them, the video optical transceiver is fully utilized in the social security dynamic monitoring system. With the construction and promotion of “Safe City Constructionâ€, “3111 Pilot Project†and “City Alarm and Surveillance Systemâ€, the video optical transceiver plays an important role in the urban public security dynamic monitoring system. In some large-scale urban public security dynamic monitoring systems, in order to ensure the quality of the video optical transceiver products, the public security department as a consumer party independently bids for unprovoked products and other important equipment. For example, in 2007, the Qingdao Municipal Public Security Bureau used a separate tendering method for the video optical transceiver products used in 1,000 monitoring sites in the first phase of the Qingdao Municipal Social Security Dynamic Monitoring System, which not only ensured the quality of the video optical transceiver but also reduced the system cost.
V. Summary
The rapid development of the video surveillance industry has brought golden opportunity for development of video optical transceivers. In the long run, the application of digital transmission will become the mainstream, and analog transmission products will exist, but may be used for short-distance transmission. With the ever-increasing traffic flow, the requirements for the integrated transmission of images, sounds, and data will increase, and digital optical transceivers will be adopted by owners as a necessary device. At the same time, the number of digitally compressed video surveillance products based on IP networks has risen in recent years. The competition between these two types of technologies has become increasingly fierce. Therefore, the alternative competitive risk is an increasingly heavy shadow behind the growth of the optical transceiver. Generally speaking, these two types of technologies have certain irreplaceability. Although the network monitoring products will play a more significant role in diverting the optical transceiver market, the long-term coexistence of these two products is also the consensus of the industry.
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