Optical fiber communication technology stands out from optical communication, becomes one of the main pillars of modern communication, and plays an important role in modern telecommunication network. As a new technology, the rapid development and wide application of optical fiber communication in recent years is rare in the history of communication, and it is also an important symbol of the world's new technological revolution and the main transmission tool of various information in the future information society.
Optical fiber is short for optical fiber. Optical fiber communication is a communication mode with light wave as information carrier and optical fiber as transmission medium. In principle, the basic material elements of optical fiber communication are optical fiber, light source and optical detector. In addition to classifying optical fibers according to manufacturing process, material composition and optical characteristics, optical fibers are often classified according to their applications, which can be divided into optical fibers for communication and optical fibers for sensing. Transmission medium optical fiber can be divided into general purpose and special purpose, and functional device optical fiber refers to the optical fiber used to complete the functions of light wave amplification, shaping, frequency division, frequency doubling, modulation and optical oscillation, and often appears in the form of some functional device. The rapid development of optical fiber communication is mainly due to its following characteristics:
(1) has large communication capacity and long transmission distance; The potential bandwidth of optical fiber can reach 20 Hz. With this bandwidth, it only takes about one second to transmit all human written materials, ancient and modern, Chinese and foreign. At present, 400Gbit/s system has been put into commercial use. The loss of optical fiber is extremely low. When the wavelength of light is about 1.55μm, the loss of optical fiber can be lower than 0.2dB/km, which is lower than that of any transmission medium at present. Therefore, the transmission distance without relay can reach tens or even hundreds of kilometers.
(2) Small signal crosstalk and good safety performance;
(3) Anti-electromagnetic interference and good transmission quality. Electric communication can't solve all kinds of electromagnetic interference problems, only optical fiber communication is free from all kinds of electromagnetic interference.
(4) The optical fiber is small in size and light in weight, which is convenient for laying and transportation;
(5) The raw materials are rich in sources and have good environmental protection, which is beneficial to saving nonferrous metal copper.
(6) Without radiation, it is difficult to eavesdrop, because the light wave transmitted by optical fiber cannot run out of the optical fiber.
(7) The optical cable has strong adaptability and long service life.
(8) Brittle texture and poor mechanical strength.
(9) Cutting and splicing of optical fibers require certain tools, equipment and technology.
(10) The diverter and coupling are not flexible.
(1 1) The bending radius of optical cable should not be too small (>; 20 cm)
(12) Power supply is difficult.
A communication method that uses light waves to transmit information in optical fibers. Because laser has obvious advantages such as high directivity, high coherence and high monochromaticity, the light wave in optical fiber communication is mainly laser, so it is also called laser-optical fiber communication.
The principle of optical fiber communication is: at the transmitting end, the transmitted information (such as voice) should be converted into an electrical signal, and then modulated on the laser beam emitted by the laser, so that the intensity of light changes with the amplitude (frequency) of the electrical signal, and then sent out through the optical fiber; At the receiving end, the detector converts the optical signal into an electrical signal and recovers the original information after demodulation.
Optical fiber communication is the main transmission means of modern communication network. Its development history is only one or two decades, and it has experienced three generations: short wavelength multimode fiber, long wavelength multimode fiber and long wavelength single mode fiber. The adoption of optical fiber communication is a major change in the history of communication. More than 20 countries, including the United States, Japan, Britain and France, have announced that they will no longer build wired communication lines and are committed to developing optical fiber communication. China optical fiber communication has entered the practical stage.
Optical fiber is a medium that transmits information from one end to the other. It is a kind of glass or plastic fiber as a transmission medium, allowing information to pass through.
Generally, the terms "optical fiber" and "optical cable" are easily confused. Most optical fibers are coated with several protective structures before use, and the coated optical cable is called "optical cable". The protective structure of the outer layer of the optical fiber can prevent the surrounding environment from damaging the optical fiber, such as water, fire and electric shock. Optical fiber can be divided into optical fiber, buffer layer and coating. Optical fiber is similar to coaxial cable, except that there is no mesh shielding layer. The center is the glass core of light propagation. In multimode fiber, the diameter of the fiber core is 1.5 μ m ~ 50 μ m, which is roughly equivalent to the thickness of human hair. The diameter of single-mode fiber core is 8 μ m ~ 10 μ m, and the fiber core is wrapped by glass cladding with lower refractive index than the fiber core, so that the fiber is kept in the fiber core. Outside is a thin plastic coat to protect the envelope. Optical fibers are usually bundled and protected by a housing. The fiber core is usually a double-layer concentric cylinder with a small cross-sectional area, which is made of timely glass, fragile and easy to break, and needs a protective layer.
Characteristics of optical fiber
Because optical fiber is a transmission medium, it can transmit data such as telephone or computer data like ordinary copper cable. The difference is that optical fiber transmits optical signals instead of electrical signals. Therefore, optical fiber has many unique advantages.
Such as: broadband, low loss, shielding electromagnetic radiation, light weight, safety and privacy.
Operation of optical fiber system
As you may know, the transmission process of any communication includes encoding → transmission → decoding. Of course, the transmission process of optical fiber system is basically the same. After the electronic signal is input, the transmitter digitally encodes the signal into an optical signal, and the light is transmitted to the receiver at the other end through the optical fiber, and the receiver decodes the signal and restores it to the original electronic signal output.
Application of optical cable
The application of optical cable can be divided into three types: professional use, general outdoor use and general indoor use. Professional applications include submarine optical cables, aerial cable on high-voltage towers, radiation-resistant optical cables in nuclear power plants and corrosion-resistant optical cables in chemical industry. However, the classification difference between general indoor use and general outdoor use varies according to the characteristics of each type of optical cable during manufacture and design.
The process of optical cable from outside to inside can be divided into empty frame, underground tunnel, direct burial, laying between pipes and indoor use.
The history of optical fiber
1880-Alexandra Graham Bell invented light beam call transmission.
1960- the invention of electricity and optical fiber
1977- First practical installation of telephone optical fiber network
1978-FORT installed optical fiber power for the first time in France.
1990- optical fiber for LAN and other short-distance transmission applications
2000-FTTH = > FTTH to Desktop
Classification of optical fiber
Optical fibers are mainly divided into the following two categories:
1) transmission point modulus class
The transmission point modulus can be divided into single-mode fiber and multimode fiber. The core diameter of single-mode fiber is very small, and it can only be transmitted in single mode at a given working wavelength, with wide transmission frequency band and large transmission capacity. Multimode fiber is an optical fiber that can transmit in multiple modes at a given working wavelength. Compared with single-mode fiber, multimode fiber has poor transmission performance.
2) refractive index distribution category
Refractive index distribution fiber can be divided into jump fiber and graded fiber. The refractive index of the core and the refractive index of the protective layer are constant. At the interface between the core and the protective layer, the refractive index changes gradually. The refractive index of graded fiber core decreases with the increase of radius, and decreases to the refractive index of protective layer at the junction of core and protective layer. The change of refractive index of fiber core is similar to parabola.
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