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The development of video optical transceivers in China is accompanied by the development of monitoring. Video optical transceivers are devices that convert one or more analog video signals into optical signals through optical fibers through various encodings. They are also divided into analog optical transceivers and digital optical transceivers. .
Analog optical transceiver
The analog optical transceiver adopts the PFM modulation technology to transmit the image signal in real time. The transmit end first performs the PFM modulation on the analog video signal, and then performs the electro-optical conversion. After the optical signal is transmitted to the receiving end, the optical-electrical conversion is performed, and then the PFM demodulation is performed to recover the video signal. Due to the use of PFM modulation technology, the transmission distance can reach 50Km or more. Through the use of wavelength division multiplexing technology, it is also possible to realize bidirectional transmission of image and data signals on a single optical fiber to meet the actual needs of the monitoring project. This analog optical transceiver also has some drawbacks:
a) production debugging is more difficult;
b) It is more difficult for a single optical fiber to achieve multi-channel image transmission, and the performance will be reduced. This analog optical transceiver can generally only transmit 4 channels of images on a single optical fiber;
c) The anti-interference ability is poor, affected by environmental factors, there is temperature drift;
d) Due to the use of analog modulation and demodulation technology, its stability is not high enough. With the increase of the use time or the change of the environment characteristics, the performance of the optical transceiver will also change, which will cause some inconvenience for the use of the project.
Digital optical transceiver
Since digital technology has obvious advantages in many aspects compared with traditional analog technologies, just as digital technology has replaced analog technology in many areas, the digitalization of optical transceivers is also an inevitable trend. There are two main digital video optical transceivers: one is an MPEG II video compression digital optical transceiver, and the other is a digital all-digital video 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 telecommunications interfaces or directly over optical fibers. Due to the use of image compression technology, it can greatly reduce the signal transmission bandwidth.
The all-digital uncompressed video optical transceiver adopts all-digital non-compression technology, so it can support any high-resolution motion and still-image transmission without distortion; overcomes the serious interference of conventional analog FM, phase modulation, and amplitude modulation optical transceivers. , Disadvantages of environmental interference, poor transmission quality, and low stability in long-term operation. And support audio two-way, data bidirectional, switch bidirectional, Ethernet, telephone and other signals in parallel transmission, convenient field wiring, plug and play. Compared with the traditional analog optical transceiver, the digital optical transceiver has obvious advantages:
1) Longer transmission distance: up to 80Km, even farther (120Km);
2) Support video lossless regeneration relay, so you can use multi-level transmission mode;
3) less interference from the environment, high transmission quality;
4) The supported signal capacity can reach 16 ways, even more (32, 64, 128).