Introduction
With the continuous improvement of satellite broadcasting and digital technology in my country’s cable television (CATV) business, it is moving towards the needs of the future information society, and is moving towards multi-channel, multi-service, The development of a multi-functional broadband integrated information network. The optical fiber technology is used in the CATV system. In particular, the application of the hybrid fiber-coaxial cable (HFC) method is not only a major change to improve the quality and reliability of the previous all-coaxial system, but also create an important The basic conditions.
Development
Since ORTEL exhibited the world’s first optical fiber CATV equipment at a CATV exhibition in California in 1987, optical fiber CATV technology and equipment have developed rapidly In the early 2009s, commercialization was achieved. At the same time, the construction of optical fiber CATV networks was upsurge in various countries around the world. After entering the 1990s, my country's cable television industry has developed rapidly. According to statistics, the number of cable TV users across the country has grown at a rate of more than 10 million per year. As of the end of June 2018, the number of cable TV subscribers reached 233.886 million, the digital cable TV subscribers reached 204.05 million, the digitization rate reached 87.24%, the digital cable TV subscribers reached 149.545 million, and the two-way network covered 169.76 million subscribers. Although the total base is large, cable TV subscribers are showing a trend of negative growth.
In the transformation of all old networks and newly built networks, optical fiber technology is almost without exception. The management department of the Ministry of Radio, Film and Television has repeatedly emphasized that optical fiber should be used when the network trunk exceeds a certain distance (about 4km). On the basis of the successful construction of the optical fiber CATV network, most areas of the country have completed the test of the optical fiber CATV integrated network and have begun to construct the optical fiber CATV integrated network. Telephone and data (computer data communication, conference TV, video on demand, TV Shopping, distance learning and diagnosis, community services, high-definition television, etc.) value-added services have made the cable television network the "last mile" of the "information highway".
With the development of the information age, people’s requirements for comprehensive information services are becoming stronger. The promotion of market and demand has provided a broad development space for fiber optic cable television networks, making it bound to Moving forward in the direction of integration and digitization, at the same time, the provincial and national networking of fiber optic cable TV has become a matter before us.
Basic Principles
A typical optical fiber CATV network structure is shown in Figure 1. The multi-channel mixed radio frequency signal from the front end of the cable TV is converted into an optical signal by an optical transmitter, and after being split by an optical splitter (when a single transmitter is used for a single receiver), it is sent to the center by optical fiber. For different optical nodes from several kilometers to dozens of kilometers, the optical receiver restores the optical signal to a multi-channel mixed radio frequency signal at the optical node and then sends it to the coaxial cable distribution network, and then enters the user. The coaxial cable cell range covered by the optical receiver is generally within 2km×2km, with 3-5 cascaded amplifiers, and the actual number of users can reach 2000. Considering the requirement of upgrading the network to an integrated network, users of optical nodes The number should be reduced to about 500 households when appropriate.
Features
It has the advantages of low loss, long transmission distance, frequency bandwidth, large transmission capacity, and anti-electromagnetic interference.
Technical indicators
The main technical indicators describing the performance of optical fiber CATV network trunks include carrier-to-noise ratio (CNR), composite second-order interference (CSO) and combined triple beat (CTB), General requirements CNR> 52dB, CSO> 60dBc, CTB
Main equipment
(1) Optical transmitter
(2) Optical receiver
(3) Optical fiber and optical cable
(4) Optical amplifier