The principle and characteristics of optical fiber

About light: light is an electromagnetic wave, the visible part of the wavelength range is: 390 ~ 760 nm, Nm) 。 Greater than 760 nm part is infrared light, less than 390 nm part is ultraviolet light. There are three kinds of the application of optical fiber: 850 nm, 1310 nm, 1550 nm. Because the speed of light in a different material is different, so the light from a substance into another substance, in the interface of two kinds of material can produce refraction and reflection. Moreover, the Angle of refraction of light changes over the Angle of the incident light. When the Angle of the incident light reach or exceed a certain Angle, the refracted light will disappear, all incident light is reflected back, this is the total reflection of light. And optical fiber transmission principle, is 'the total reflection of light. ' Different substances on the same wavelength of light refraction Angle is different, Different materials have different light refractive index) , the same material with different wavelengths of light refraction Angle is also different. Using optical fiber communication is optical fiber communication and optical fiber communication is based on the above principle. First is optical transmitter in optical fiber communication convert electrical signals into light signals, and coupling technology light signals into optical fiber, the maximum and the optical fiber as a transmission channel of light signal, as the light transmission path between the transmitter and the receiver. Optical receiver to convert optical signals to electrical signals. Optical fiber transmission theory is divided into mode theory and the theory of light. The light as an electromagnetic wave, the research on the rules of electromagnetic waves in the optical fiber transmission, transmission mode, the field of optical fiber structure, the transmission constant and the cut-off conditions. Fiber today, the characteristics of optical fiber has become indispensable to our daily life, as a mainstream way of broadband access, with wide frequency band, large capacity of communication, low dissipation, relay, long distance, high fidelity, strong anti-interference ability and adaptability, small volume, light weight, wide raw material sources, price is low wait for an advantage. 1, the transmission band width, large capacity of communication by the information theory, the higher the carrier frequency, the greater the communication capacity. Now use the light frequency 10000 ~ 100000 times higher than the microwave frequency and so can increase the communication capacity of about 10000 ~ 100000 times. Optical fiber, for example, can accommodate hundreds MHz TV channel, transmission of information up to billions of bits per second, tens of thousands of times more than the current line, great potential and can basically meet the current and future data transmission, video transmission, such as demand for bandwidth. 2, low dissipation, long distance relay at present, a lot of the optical fiber used for SiO2 ( Quartz) Department of optical fiber, mainly by the purity to reduce the loss of the glass fiber. Due to the high purity of SiO2 glass made of medium, so the loss of the fiber is extremely low. In 1. 55 mu m light wavelength near loss minimum, can be as low as zero. 2 db/km, close to theoretical limit. Due to the low loss optical fiber, so relay distance can be very long, can reduce the number of Repeaters in the communication line, reduce costs and improve the quality of communication. In addition, the optical fiber transmission loss has two characteristics: one is in the cable TV channels with the same loss, don't need like cable trunk must introduce equalizer for equilibrium; 2 it is hardly varies with temperature, its loss do not have to worry about the main level fluctuations caused by environment temperature change. 3, strong anti-jamming capability for optical fiber is the basic composition of quartz, only the light, not conductive, the effect of electromagnetic field, in which the light signal transmission is not affected by electromagnetic field, so the optical fiber transmission to the electromagnetic interference, industrial interference has a strong ability to resist. Also because of this, the optical fiber transmission of signals to be tapped, thus conducive to secrecy. 4, small volume, light weight, flexible fiber diameter is only 0. 1 mm or so, made after the cable, finer than cable diameter, weight is light, can save installation space, and good flexible, transportation and installation easier. 5, performance, resources rich fiber has high and low temperature resistant capability is strong, high tensile strength, resistance to chemical corrosion, transfer, good stability, high reliability, etc. Suitable for application in the occasion of climate and installation conditions. 6, the cost is falling due to the production of optical fiber materials ( Quartz) Source is very rich, with the progress of technology, the cost will be further reduced; The copper raw material for cable co. , LTD. , the price will be more and more high. Obviously, the optical fiber transmission will be dominant, establish a cable television network in the province, and the state of the main means of transport.