History and advantages of fiber optic transmission
It was not until 1960, US scientists Maiman invented the world's first laser for optical communications provide a good source. Then twenty years, people were optical transmission media research, and finally made a low-loss optical fiber, thus laying the cornerstone of optical communications. Since then, the optical communications entered a stage of rapid development.
Optical fiber transmission has many outstanding advantages:
Represents the size of the transmission band width capacity. The higher the frequency of the carrier, the bandwidth of the transmitted signal can be greater. In the VHF band, the carrier frequency is 48.5MHz ~ 300Mhz. Bandwidth of about 250MHz, can only transmit 27 sets of television and dozens of sets of FM radio. Visible light frequencies up 100000GHz, higher than the VHF band over one hundred times. Although the optical fiber to different frequencies of light have different loss, so that the bandwidth is affected, but in the lowest frequency band width of the depletion region can also reach 30000GHz. Currently only a single light source bandwidth which a small part (multimode fiber band of about a few hundred megahertz, a good single-mode fiber up to 10GHz or more), the use of advanced coherent optical communication can be arranged within 2000 light 30000GHz range carrier carried WDM, can accommodate one million channels.
In the system consisting of a coaxial cable, the cable is preferably at 800MHz signal transmission loss per kilometer are more than 40dB. In contrast, much smaller loss of optical fiber, optical transmission 1.31um per kilometer transmission loss 0.35dB below 1.55um if light, smaller loss per kilometer, up to 0.2dB below. This power loss than the coaxial cable one hundred million times smaller, so that it can transmit much farther distances. In addition, there are two characteristics of optical fiber transmission loss, one has all the cable channels in the same loss, do not like the trunk cable must be introduced as a balanced equalizer; the second is the loss hardly varies with temperature, do not worry because changes in ambient temperature causes fluctuations in mains level.
Because fiber is very fine, single-mode fiber core diameter is generally 4um ~ 10um, only the outer diameter of 125um, plus waterproof layer, ribs, jacket, etc., with 4 to 48 fibers consisting of cable diameter less than 13mm, 47mm in diameter than standard coaxial cable is much smaller, with optical fibers are glass fibers, the proportion of small, it has a small diameter, light weight, very easy to install.
Strong anti-jamming capability
Because the basic components of the fiber is quartz, only pass light, non-conductive, action against electromagnetic fields affect signal transmission in which the light from electromagnetic fields, so fiber transmission of electromagnetic interference, industry has a strong ability to resist interference. Precisely because of this, the signal transmission in the fiber can not easily be tapped, thus conducive to secrecy.
Because optical transmission relay amplification generally do not need, not because of the introduction of new nonlinear distortion amplification. As long as the laser is linear, high-fidelity transmission of television signals can be. Actual tests show good combination of three differential amplitude modulated carrier fiber system to shoot ratio C / CTB in more than 70dB, 60dB intermodulation indicators also cM, much higher than the general nonlinear distortion indicators cable trunk system.
We know that, with the reliability of a system composed of the number of devices of the system concerned. The more devices, the greater the chance of failure. Because the device contains a small number of fiber-optic system (unlike the dozens of cable systems that require an amplifier), naturally high reliability, coupled with fiber optic equipment life is very long, trouble-free working hours up to 500,000 to 750,000 hours, which is the shortest life expectancy in the laser optical transmitter, the lowest life expectancy are more than 100,000 hours. It is a well-designed, properly installed debugging performance fiber optic system is very reliable.
Costs continue to decline
At present, it was suggested that a new Moore, also known as the laws of optics (Optical Law). The law states that the bandwidth of optical fiber transmission of information, every six months doubled, while lower prices doubled. Development of optical communication technology for the development of broadband Internet technology has laid a very good foundation. This fiber-optic transmission cleared the last obstacle for large cable systems. Because the production of the fiber material (quartz) is very rich sources, as technology advances, the cost will be further reduced; and limited cable copper raw materials needed, the price will be higher. Clearly, the future will account for fiber optic transmission absolute advantage, as the establishment of the province, as well as the main means of transmission of the national cable networks.