Video optical transceiver is a device that converts 1 to multi-channel analog video signals into optical signals through various codes and transmits them through optical fiber media. It is mainly used in the field of video security monitoring in China. Since the video signal is converted into an optical signal through two technologies, analog conversion and digital conversion, the video optical transceiver is divided into an analog optical transceiver and a digital optical transceiver.
Analog Optical Transceiver
The analog optical transceiver adopts the PFM modulation technology to transmit the image signal in real time. The transmitter first performs PFM modulation on the analog video signal, and then performs electrical-to-optical conversion. After the optical signal is transmitted to the receiver, performs optical-to-electrical conversion, and then performs PFM demodulation to restore 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, the bidirectional transmission of image and data signals can also be realized on one optical fiber to meet the actual needs of monitoring projects. This analog optical transceiver also has some disadvantages:
a) Production debugging is difficult;
b) It is difficult to realize multi-channel image transmission with a single fiber, and the performance will be degraded. Generally, this analog optical transceiver can only transmit 4-channel images on a single fiber;
c) The anti-interference ability is poor, which is greatly affected by environmental factors and has temperature drift;
d) Since the analog modulation and demodulation technology is used, its stability is not high enough. With the increase of use time or the change of environmental characteristics, the performance of the optical transceiver will also change, which brings some inconvenience to the project.
Digital Optical Transceiver
Compared with traditional analog technology, digital technology has obvious advantages in many aspects, so just as digital technology has replaced analog technology in many fields, the digitization of optical transceiver is also an inevitable trend. There are two main technical modes of digital video optical transceiver: one is MPEG II image compression digital optical transceiver, and the other is full digital non-compressed video optical transceiver.
Image compression Digital optical transceivers generally use MPEG II image compression technology, which can compress moving images into N×2Mbps data streams and transmit them through standard telecommunication communication interfaces or directly through 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 uncompressed technology, so it can support any high-resolution motion and still image distortion-free transmission; it overcomes the serious intermodulation interference when the conventional analog frequency modulation, phase modulation, and amplitude modulation optical transceivers transmit multiple signals at the same time. , Easily affected by environmental interference, poor transmission quality, low long-term work stability and other shortcomings. And it supports the parallel transmission of audio bidirectional, data bidirectional, digital bidirectional, Ethernet, telephone and other signals, convenient on-site wiring, plug and play. Compared with traditional analog optical transceivers, digital optical transceivers have obvious advantages:
a) Longer transmission distance: up to 80Km, or even further (120Km);
b) Support video lossless regeneration relay, so multi-level transmission mode can be used;
c) Less interference from the environment and high transmission quality;
d) The supported signal capacity can reach 16 channels or even more (32 channels, 64 channels, 128 channels).