Video optical transmitter is the equipment that converts 1 to multi-channel analog video signal into optical signal through various codes and transmits it through optical fiber medium. It is mainly used in the field of video security monitoring in China. Because the video signal will be converted into optical signal through analog conversion and digital conversion two technologies, so the video optical end machine is divided into analog optical end machine and digital optical end machine.
Analog optical end machine
The analog optical terminal uses PFM modulation technology to transmit image signal in real time. The transmitter first carries out PFM modulation of the analog video signal, and then carries out electro-optical conversion. After the optical signal is transmitted to the receiver, it carries out opto-electric conversion, and then carries out PFM demodulation to recover the video signal. Due to the adoption of PFM modulation technology, the transmission distance can reach 50Km or more. By using WDM technology, bidirectional transmission of image and data signal can be realized on one optical fiber, which can meet the actual demand of monitoring engineering. This analog optical terminal also has some disadvantages:
A) Difficult production debugging;
B) It is difficult for a single optical fiber to realize multi-channel image transmission and its performance will decline. This kind of analog optical terminal machine can only transmit 4-channel images on a single optical fiber;
C) Poor anti-interference ability, greatly affected by environmental factors, with temperature drift;
D) Due to the adoption of analog modulation and demodulation technology, its stability is not high enough. With the increase of use time or the change of environmental characteristics, the performance of optical terminal machine will also change, bringing some inconvenience to engineering use.
Digital optical transmitter
As digital technology has obvious advantages over traditional analog technology in many aspects, just as digital technology has replaced analog technology in many fields, the digitalization of optical terminal machine is also an inevitable trend. Digital video optical transceiver mainly has two technical methods: one is MPEG II image compression digital optical transceiver, the other is all digital uncompressed video optical transceiver.
Image compression Digital optical end machine generally uses MPEG II image compression technology, it can compress the active image into N×2Mbps data flow through the standard telecommunication communication interface transmission or directly through the optical fiber transmission. Because of the image compression technology, it can greatly reduce the signal transmission bandwidth.
All-digital uncompressed video optical terminal adopts all-digital uncompressed technology, so it can support any high resolution motion and still image transmission without distortion. It overcomes the disadvantages of serious interference, easy to be affected by environmental interference, poor transmission quality and low long-term stability of analog frequency modulation, phase modulation and amplitude modulation optical terminal. And support audio bidirectional, data bidirectional, switching volume bidirectional, Ethernet, telephone and other signals parallel transmission, convenient field wiring, plug and play. Compared with traditional analog optical terminal, digital optical terminal has obvious advantages:
1) Long transmission distance: up to 80Km, or even farther (120Km);
2) Support video lossless regenerative relay, so it can adopt multi-level transmission mode;
3) Less environmental interference, high transmission quality;
4) Supported signal capacity up to 16 channels, or more (32 channels, 64 channels, 128 channels).