The role of optical fiber is "communication". Optical fiber network is the carrier of optical fiber communication, so the main function of optical fiber is communication; because optical fiber communication has the advantages of wide frequency band, low attenuation, light weight, strong anti-interference ability, large capacity, high fidelity, and strong confidentiality, it Become an important method of modern communication technology.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
Optical fiber is the abbreviation of optical fiber. It is a fiber made of glass or plastic and can be used as a light transmission tool. The transmission principle is "total reflection of light".
Optical fiber network is the carrier of optical fiber communication, so the main function of optical fiber is communication.
Optical fiber has many uses, mainly used to realize optical communication. Because optical fiber communication has the characteristics of low attenuation, anti-interference, large capacity, and strong confidentiality, it has become an important method of modern communication technology.
Optical fiber transmission has many outstanding advantages:
Frequency bandwidth
The wide and narrow representative of the frequency band The size of the transmission capacity. The higher the frequency of the carrier, the wider the bandwidth over which the signal can be transmitted. In the VHF band, the carrier frequency is 48.5MHz~300Mhz. The bandwidth is about 250MHz, which can only transmit 27 sets of TV sets and dozens of sets of FM radio. The frequency of visible light reaches 100,000 GHz, which is more than one million times higher than the VHF frequency band. Although the frequency bandwidth is affected because optical fibers have different losses for light of different frequencies, the frequency bandwidth in the lowest loss area can also reach 30,000 GHz. The bandwidth of a single light source only accounts for a small part of it (the frequency band of multi-mode fiber is about a few hundred MHz, and a good single-mode fiber can reach more than 10 GHz). Using advanced coherent optical communication, 2,000 optical carriers can be arranged in the 30,000 GHz range , performs wavelength division multiplexing and can accommodate millions of channels.
Low loss
In a system composed of coaxial cables, the best cables have a loss of more than 40dB per kilometer when transmitting 800MHz signals. In comparison, the loss of optical fiber is much smaller. When transmitting 1.31um light, the loss per kilometer is less than 0.35dB. If it transmits 1.55um light, the loss per kilometer is even smaller, up to less than 0.2dB. This is 100 million times less than the power loss of coaxial cable, allowing it to transmit much farther.
In addition, optical fiber transmission loss has two characteristics:
First, it has the same loss in all cable TV channels and does not need to be introduced like cable trunks The equalizer performs equalization;
The second is that its loss almost does not change with temperature, so there is no need to worry about fluctuations in the mains level caused by changes in ambient temperature.
Light weight
Because the optical fiber is very thin, the core diameter of single-mode optical fiber is generally 4um~10um, and the outer diameter is only 125um. The diameter of the optical cable composed of 4 to 48 optical fibers is less than 13mm, which is much smaller than the standard coaxial cable diameter of 47mm. In addition, the optical fiber is glass fiber and has a small specific gravity. It has the characteristics of small diameter and light weight, and is very convenient to install.
Strong anti-interference ability
Because the basic component of optical fiber is quartz, it only transmits light, does not conduct electricity, and is not affected by electromagnetic fields. The optical signal transmitted in it is not Affected by electromagnetic fields, optical fiber transmission has strong resistance to electromagnetic interference and industrial interference. Because of this, the signals transmitted in the optical fiber are not easy to be eavesdropped, which is conducive to confidentiality.
High fidelity
Because optical fiber transmission generally does not require relay amplification, new non-linear distortion will not be introduced due to amplification. As long as the linearity of the laser is good, TV signals can be transmitted with high fidelity. Actual tests show that the third beat ratio C/CTB of the carrier combination of a good AM optical fiber system is above 70dB, and the intermodulation index cM is also above 60dB, which is much higher than the nonlinear distortion index of the general cable trunk system.
Reliable working performance
We know that the reliability of a system is related to the number of devices that make up the system. The more equipment there is, the greater the chance of failure. Because the optical fiber system contains a small number of equipment (unlike the cable system that requires dozens of amplifiers), the reliability is naturally high. In addition, the life of the optical fiber equipment is very long, with a trouble-free working time of 500,000 to 750,000 hours. Among them, the laser in the optical transmitter has the shortest life, and the minimum life is more than 100,000 hours. Therefore, the working performance of a well-designed, correctly installed and debugged optical fiber system is very reliable.
Costs keep falling
Someone proposed a new Moore’s Law, also called Optical Law. This law states that the bandwidth of optical fiber transmission of information doubles every 6 months, while the price decreases by a factor of 1. The development of optical communication technology has laid a very good foundation for the development of Internet broadband technology. This clears the last hurdle for large cable television systems to adopt fiber optic transmission. Since the source of materials (quartz) for making optical fibers is very abundant, with the advancement of technology, the cost will be further reduced; while the copper raw materials required for cables are limited, the price will become higher and higher. Obviously, optical fiber transmission will have an absolute advantage in the future and become the most important transmission method for establishing provincial and even national cable TV networks.
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