The modern communications network's 3 big props are the fiber optic communications, the satellite communication and the radio traffic, but the fiber optic communications is a main body, this is because the fiber optic communications itself has many prominent merits:
(1) the band width, the message capacity is big. The optical fiber may the use band width approximately be the 50000GHz,1987 year is operational 1. the 7Gb/s fiber optic communications system, a pair of optical fiber can simultaneously transmit 24192 groups telephones, the 2.4Gb/s system, can simultaneously transmit 30000 multiple telephones. The band width, regarding transmits each kind of wideband information to have the very vital significance, otherwise, will be unable to satisfy in the future the wide band synthesis service digit network (B-ISDN) need to develop.
(2) loses lowly, the relaying distance is long. At present is practical the silica fiber the loss to be possible to be lower than 0.2dB/km, lowers compared to other any transmission medium's loss, if the future will use the non-quartz department to be extremely low loses the optical fiber, its theoretical analysis will lose may drop to 10-9dB/km. Because optical fiber's loss is low, can therefore realize the relaying distance to be long, is composed the fiber optic communications system by the silica fiber most major most and medium to be possible to amount to more than 200 kilometers following the distance, is extremely low by the non-quartz department loses the communications system which the optical fiber is composed, its most major most and medium following is away from may amount to several thousand even several thousand kilometers, this regarding reduces the seabed correspondence the cost, to enhance the reliability and the stability has the special significance.
(3) anti-electromagnetic interference. The optical fiber is the insulator material, it not nature thunder and lightning disturbance, ionized layer change with sun-spot activity disturbance, also not industry electric appliance's and so on electric railway lead and high pressure unit disturbances, but also available it parallel erects or and the electric power conductor compound constitution compound fiber optics with the high-voltage transmission line.
(4) the non-crosstalk disturbance, the secrecy is good. The light wave transmits in the fiber optics, divulges very difficultly from the optical fiber, even if in the turning, the bevelling radius is very small time, leaks off the light wave is also very weak, if spreads a deadening agent effect in the optical fiber or the fiber optics surface to be better, like this, even if in the fiber optics the optical fiber total are many, may also realize the non-crosstalk disturbance, outside fiber optics, is also unable the information which intercepts in the optical fiber to transmit.
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(5) the optical fiber line diameter is thin, the weight is light, is soft, causes the transmission system to occupy the space to be small, the solution underground duct crowded question, saves the underground duct construction investment. In addition, optical fiber's weight is light, the fiber optics importantly is much lighter than the electric cable.
