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At present, security video surveillance still uses coaxial cables as the transmission medium for short-distance signal transceiving; with the impact of IP, TCP/IP protocol network transmission methods are also increasingly applied. However, no matter which transmission method, it can not meet the transmission needs of modern security. Optical terminal as a transmission medium terminal equipment, it becomes important in the entire transmission. 
Optical transceiver classification and principle
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 data transmission standard for trunk lines, typically at 2.048 MbPS, which is adopted 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. Simulated optical transceiver The analog optical transceiver uses PFM modulation technology to transmit image signals 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 around 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. The digital optical transceiver has obvious advantages in many aspects compared with the traditional analog technology. Therefore, 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. 
The image compression digital optical transceiver generally adopts MPEGII image compression technology. It can compress moving images into N×2Mbps data streams and transmit them through a standard telecommunication interface or directly through 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, thanks to the N×2Mbps standard interface, it is possible to use the rich channels of existing telecommunication transmission equipment to transmit surveillance 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 1-2S delay 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.
Selection
From the signals sent to the optical fiber, optical transceivers can be divided into analog optical transceivers based on analog technology and digital optical transceivers based on digital technology. The working principle of analog optical transceiver is nothing more than modulation, demodulation, filtering and signal mixing. Whether it is LED or LD, the photoelectric modulation characteristics thereof are not linear, and inevitable problems such as distortion, interference, and other analog processing are inevitable in the signal transmission process, and there are insurmountable technologies in terms of large-capacity transmission and multi-service mixed transmission. difficulty.
With the development of the times and the increasing requirements of users for security precautions, surveillance optical transceivers have been more and more widely used in the field of security, and the technology for monitoring optical transceivers has become more and more mature. Currently, optical transceivers for monitoring can already be implemented on one core fiber. On the transmission of multiple video, audio, data, telephone, Ethernet, E1 signals, alarms and other signals. 
Use, maintenance and maintenance
(1) In the use of the optical transceiver, it is necessary to ensure that the laser components and the photoelectric conversion module of the continuous and normal power supply optical transceiver are extremely immune to the impact of the instantaneous pulse current, so it is not suitable to frequently switch on and off. The UPS power supply should be configured in the center front-end room of the optical transceiver and the 1550nm optical transmitter optical amplifier set-up point to protect the laser module and protect the photoelectric conversion module from the pulsed high current.
(2) Keep a ventilation, heat dissipation, moisture-proof and tidy work environment in use of the optical transceiver. The laser assembly of the optical transmitter is the heart of the equipment and requires high working conditions. In order to ensure the normal operation of the equipment, the manufacturer is in the equipment. The cooling and heat removal system is set up, but when the ambient temperature exceeds the allowable range, the equipment cannot work normally. Therefore, in hot season, when the central equipment room has more heating equipment and the ventilation and cooling conditions are poor, it is better to install the air conditioning system. Ensure that the optical transceiver works normally.
The core diameter of the optical fiber core is in the micron range. Fine dust enters the pigtail active interface and blocks the propagation of the optical signal, causing a significant drop in optical power and a reduction in the signal to noise ratio of the system. This type of failure rate is approximately 50%. Cleanliness is also very important.
(3) Operation and recording of the optical transceivers The optical transceivers are equipped with microprocessors to monitor various operating parameters of the system's internal operating status acquisition module, and are displayed visually through the LED and VFD display systems, in order to promptly notify the check-in personnel. The sound transmitter and light alarm system is set up in the optical transmitter. As long as maintenance personnel determine the cause of the fault based on the operating parameters and perform the processing in time, the normal operation of the system can be guaranteed.
Video Optical Technology Principle and Selection Maintenance
A video optical transceiver is a device that converts one to multiple video signals through various encodings and converts the optical signals into optical signals through an optical fiber medium. Since the video signal is converted into an optical signal, both the analog and digital conversion technologies are used. Optical transceivers are divided into analog optical transceivers and digital optical transceivers. The principle of the optical transceiver is to modulate the signal to the light and transmit the video through the optical fiber.