Optical fiber communication technology(optical fiber communications) has stood out from optical communications and become one of the main pillars of modern communicationsModern telecommunication networkPlays an important role in.As an emerging technology, optical fiber communication has developed rapidly and applied widely in recent years, which is rare in the history of communication. 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.
Chinese name
Optical fiber communication
Foreign name
optical fiber communications
Major code
five hundred and ninety thousand three hundred and nine
Optical fiberIt is the abbreviation of optical fiber.Optical fiber communication is based onlight waveAsinformation carrier , using optical fiber as the 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 their manufacturing process, material composition and optical characteristics, optical fibers are often classified according to their applications, which can be divided intoCredit optical fiberandOptical fiber for sensing。Transmission mediumThere are two types of optical fiber: general purpose and special purpose. The functional component optical fiber refers to the optical fiber used to amplify, reshapefrequency division, frequency doubling, modulation, optical oscillation and other functions of optical fiber, and often in the form of a functional device.
Optical fiber communication is a communication method that uses optical waves as carriers and optical fibers as transmission media to transmit information from one place to another. It is called "wired" optical communication.Nowadays, optical fiber has become the main transmission mode in the world communication because of its transmission frequency bandwidth, high anti-interference and small signal attenuation, which are far superior to the transmission of cable and microwave communication.
In 1966, Charles Kao, a British Chinese, published a paper that proposed to use quartz to make glass fiber (optical fiber), with a loss of up to 20dB/km, which can realize high-capacity optical fiber communication.At that time, only a few people in the world believed, such as the British Standard Telecommunication Laboratory (STL), the American Corning Glass Company, Bell Laboratory and other leaders.In 2009, Kao Kun won the Nobel Prize for his invention of optical fiber.In 1970, Corning Company developed quartz optical fiber with loss as low as 20dB/km and length of about 30m.In 1976, Bell Laboratory established an experimental line in Atlanta, Washington, with a transmission rate of only 45Mb/s, which can only transmit hundreds of calls, while 1800 calls can be transmitted with a coaxial cable.Because there is no laser for communication at that time, but light emitting diode (LED) is used as the light source for optical fiber communication, the speed is very low.Around 1984, the semiconductor laser for communication was successfully developed, and the optical fiber communication rate reached 144Mb/s, which can transmit 1920 calls.In 1992, the transmission rate of one optical fiber reached 2.5Gb/s, equivalent to more than 30000 telephones.In 1996, lasers of various wavelengths were successfully developed, which can realize multi wavelength and multi-channel optical fiber communication, namely the so-called "Wavelength Division Multiplexing" (WDM) technology, that is, to transmit multiple optical signals of different wavelengths in one fiber.So the transmission capacity of optical fiber communication is doubled.In 2000, using WDM technology, the transmission rate of one optical fiber reached 640Gb/s.Some people have great doubts that Kao Kun invented optical fiber in 1976 and won the Nobel Prize in 2010.In fact, it can be seen from the above development history of optical fiber that although the capacity of optical fiber is very large, it cannot play the role of super capacity of optical fiber without high-speed lasers and microelectronics.The speed of electronic devices has only reached the order of gigabit per second, and the emergence of high-speed lasers with various wavelengths has made fiber transmission reach the order of terabit per second (1Tb/s=1000 Gb/s). Only then did people realize that "the invention of fiber has triggered a revolution in communication technology!"
Advantages and disadvantages
（1）Communication capacityLarge transmission distance;Potential of one fiberbandwidthUp to 20THz.With such bandwidth, it only takes about one second to complete the transmission of all the written materials of mankind at all times and in all countries.The 400Gbit/s system has been put into commercial use.The loss of optical fiber is extremely lowwavelengthAround 1.55 μ m,Quartz fiberThe loss can be lower than 0.2dB/km, which is more than any transmissionmediumThe loss is low.Therefore, the transmission distance without relay can reach tens or even hundreds of kilometers.
(2) Small signal interference and good security performance;
(3) Antielectromagnetic interference The transmission quality is good. Electric communication cannot 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) Rich material sources and good environmental protection are conducive to saving non-ferrous copper.
(6) There is no radiation and it is difficult to eavesdrop, because the light wave transmitted by the optical fiber cannot run out of the optical fiber.[1]
(7)optical cableStrong adaptability and long service life.
(8) The texture is brittle and the mechanical strength is poor.
(9) Certain tools, equipment and technologies are required for cutting and connecting optical fibers.
(11) The bending radius of optical fiber and cable shall not be too small (>20cm)
(12) Power supply is difficult.
A communication mode that uses light waves to transmit information in optical fiberslaserIt 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
Principle and Application
The principle of optical fiber communication is: at the sending end, the transmitted information (such as voice) should first be converted into an electrical signal, and then modulated toLaserOn the emitted laser beam, the intensity of light changes with the amplitude (frequency) of the electrical signal, and is sent out through the optical fiber;At the receiving end, the detector converts the optical signal into an electrical signal after receiving it, and recovers the original information after demodulation
With the increasingly updated transmission speed of information technology, optical fiber technology has been widely valued and applied.In the multi microcomputer elevator system, the application of optical fiber fully meets the requirements of correct, reliable, high-speed transmission and processing of a large number of data communications.The application of optical fiber technology in the elevator has greatly improved the response speed of the entire control system and the parallel group control performance of the elevator system.Elevator.The optical fiber communication device used on the is mainly composed of light source, photoelectric receiver and optical fiber.
light source
The signal output by the microcomputer control system is electrical signal, while the optical fiber system transmits optical signal. Therefore, in order to transmit the electrical signal generated by the microcomputer system in the optical fiber, first convert the electrical signal into optical signal.Light source is such an electro-optic converter.
The light source first converts the electrical signal into an optical signal, and then sends the optical signal to the optical fiber.Light source plays a very important role in optical fiber system.Incandescent lamps, lasers and semiconductor light sources can be used as optical fiber light sources.The semiconductor light source uses the PN junction of semiconductor to convert electric energy into light energy. The commonly used semiconductor light sources are semiconductor light-emitting diodes (LEDs) and laser diodes (LDs).
Semiconductor light source has been widely used in optical fiber transmission system because of its small size, light weight, simple structure, easy to use, and easy compatibility with optical fiber.
Photoelectric receiver
Before the optical signal transmitted in the optical fiber is received by the microcomputer system, it must first be restored to the corresponding electrical signal.This conversion is achieved through an optical receiver.The function of the optical receiver is to convert the optical signal transmitted from the optical fiber into an electrical signal, and then send the electrical signal to the control system for processing.According to the principle of photoelectric effect, the optical receiver irradiates the PN junction of the semiconductor with light. The PN junction of the semiconductor will generate carriers after absorbing the light energy, thus generating the photoelectric effect of the PN junction, so as to convert the optical signal into an electrical signal.Semiconductor receivers used in optical fiber systems mainly include semiconductor photodiodes, phototransistors, photomultiplier tubes and photocells.Photoelectric triode can not only transform the incident light signal into electrical signal, but also amplify the electrical signal, so that it can be well matched with the interface circuit of the control system. Therefore, the photoelectric triode is most widely used.
Optical fiber
Optical fiber is the transmission channel of optical signal and the key material of optical fiber communication.
The optical fiber consists of core, cladding, coating layer and jacket, which is a symmetric cylinder with multi-layer dielectric structure.The main body of the fiber core is silicon dioxide, which is mixed with trace other materials to improve the optical refractive index of the material.There is a cladding outside the core, which has a different optical refractive index from the core. The optical refractive index of the core is high to ensure that the optical signal is mainly transmitted in the core.The coating outside the cladding is mainly used to increase the mechanical strength of the optical fiber, so as to prevent the optical fiber from external damage.The outermost layer of optical fiber is the jacket, which also plays a protective role.
The two main characteristics of optical fiber are attenuation and dispersion.Loss is the attenuation or dispersion of optical signal in unit length, expressed in db/km. This parameter relates to the transmission distance of optical signal. The greater the loss, the shorter the transmission distance.Multi microcomputer elevator control systems generally have short transmission distance, so plastic optical fiber is mostly used to reduce costs.The dispersion of optical fiber is mainly related to pulse broadening.In Mitsubishi elevator control system, optical fiber communication is mainly used for data transmission between group control and single elevator and between two parallel single elevators.The optical fiber device used by Mitsubishi Elevator is mainly composed of light source, optical receiver and optical fiber. The light source and optical receiver are enclosed in the fixed plug of the optical fiber connector, and the optical fiber is connected with the moving plug.
[2]WDM (Wavelength Division Multiplexing) technology refers to the technology that uses multiple lasers to transmit multiple different wavelengths of light on the same fiber at the same time.It can greatly improve the transmission capacity of optical fiber transmission system.1.6 Tbit/s WDM system has been commercialized on a large scale.In order to further improve the capacity of optical fiber transmission, DWDM (Dense Wavelength Division Multiplexing) has become the main research object in the world since 1995. Lucent Bell Laboratories believes that the capacity of commercial DWDM systems can reach 100 Tbit/s.DWDM based on 10 Gbit/s has gradually become the mainstream of the core network among many operators in China.In addition to the increasing number of wavelengths and transmission capacity, the optical transmission distance of the DWDM system has also increased from 600 km to more than 2000 km.In addition, Coarse Wavelength Division Multiplexing (CWDM) also came into being in the expansion of metro optical transmission network, which has the advantages of super capacity, short distance transmission and low cost.Researchers also found that wavelength division multiplexing of multiple OTDM signals can greatly improve the transmission capacity.As long as it is properly combined, transmission above Tbit/s can be realized. Therefore, it has become the development direction of future optical fiber communication.Most of the transmission experiments in the laboratory that exceed 3 Tbit/s are implemented in this way.
Optical soliton communication technology
[3]Light is a special kind of ultrashort optical pulse on the order of ps, and its waveform and speed remain unchanged after long distance transmission through optical fiber.Optical soliton communication is to use optical solitons as a carrier to realize long-distance distortion free communication. Under the condition of zero error code, information transmission can reach ten thousand miles.Many experiments show that it can be used for submarine optical cable communication, and it is suitable for combining with WDM system to form ultra-high speed and large capacity optical communication. When the single channel rate reaches above 40 Gbit/s, the advantages of optical soliton communication can be fully reflected.
Optical fiber access technology
PON technology can be combined with a variety of technologies, such as ATM SDH and Ethernet, to produce APON, GPON and EPON respectively. In contrast, EPON inherits the advantages of Ethernet and has relatively low cost. After being combined with fiber technology, EPON is not only limited to the local area network, but also extended to the metropolitan area network, or even the WAN.Fiber to the home also uses EPON technology;GPON has the most advantage in supporting circuit switching services, and can make full use of existing SDH technology, but the technology is complex and the cost is high;APON will be used to implement the FTTH scheme.
working process
Sending: The CPU serializes the parallel data through a special IC chip, and inserts the corresponding bit code (start, stop, check bit, etc.) according to the communication format. The output TXD sends the signal to the optical fiber connector (i.e. the fixed plug), and then the light source in the optical fiber connector performs the electro-optical conversion. The converted optical signal sends the optical signal to the optical fiber through the optical fiber moving plug,The optical signal propagates forward in the optical fiber.
Receiving: the optical signal from the optical fiber is sent to the receiver of the fixed plug through the moving plug of the optical fiber connector. The receiver will restore the received optical signal optically and electrically to obtain the corresponding electrical signal, which is sent to the RXD input terminal of the special IC chip. After the serial data is changed to the parallel data by the special IC chip, it is transmitted to the CPU.
application area
The application field of optical fiber communication is very wide, mainly used for local trunk lines. The advantages of optical fiber communication can be fully utilized here, gradually replacing cables, and widely used.It is also used for long-distance trunk communication. In the past, cablemicrowaveSatellite communication, now gradually using optical fiber communication and forming a globally dominant bit transmission method;For global useCommunication networkPublic telecommunication networks in various countries (such as China's national primary trunk lines, provincial secondary trunk lines and sub county branch lines);It is also used for high-quality color TV transmission, industrial production site monitoring and dispatching, traffic monitoring, control and command, urban cable TV network, publicantenna(CATV) system forOptical LANAnd others such as in aircraft, spacecraft, ships, underground mines, power sector, military and corrosive and radioactive use.
The optical fiber transmission system is mainly composed of optical transmitter, optical receiver, optical cable transmission line, optical repeater and various passive optical devices.To achieve communication, baseband signals must also pass through the electrical terminalMachine pairThe signal is processed and sent to the optical fiber transmission system to complete the communication process.
It is suitable for optical fiberAnalog communication systemMedium, but also suitable for optical fiberDigital communication systemandData communication system。In the optical fiber analog communication system, the electrical signal processing refers to the baseband signal amplification, pre modulation and other processing, while the electrical signal back processing is the reverse process of the transmitter processing, that is, demodulation, amplification and other processing.In optical fiberDigital communication systemIn, electrical signal processing refers to amplification, sampling and quantization of baseband signals, that isPulse code modulation(PCM) and line code type coding processing, while the back processing of electrical signals is also the reverse process of the originator.For data optical fiber communication, electrical signal processing mainly includes signal amplification, andDigital communication systemThe difference is that it does not need code transformation.
Professional settings
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Training objectives
This major trains students to be able to engage in the planning and construction of optical fiber network engineeringSDHApplied talents in system commissioning and maintenance, engineering maintenance of telecommunication core network and access network.With strong cableoptical cableThe ability of design and construction, line planning budget, and comprehensive professional ability in the installation, commissioning and maintenance of optical fiber communication equipment and related fields.
Engaged in optical fiber communicationLine engineeringAnd access network design, construction, budget preparation andProject supervision；Installation, commissioning, operation and maintenance of optical fiber communication equipment;Communication network planning, design, construction, supervision, etc.
development
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Optical fiber communication is the main means of transmission in modern communication networks. It has experienced three generations: short wavelength multimode fiber, long wavelength multimode fiber and long wavelength single-mode fiber. The use 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 not build cablesCommunication lineAnd devoted to the development of optical fiber communicationChina Optical Fiber CommunicationIt has entered the practical stage
The birth and development of optical fiber communication istelecomAn important revolution in history andsatellite communication、mobile communicationThey are listed as technologies in the 1990s.After entering the 21st century, due to the rapid development of Internet services and the growth of audio, video, data and multimedia applications, there is a more urgent demand for high-capacity (ultra high speed and ultra long distance) lightwave transmission systems and networks.
Optical fiber communication uses light waves ascarrierIt is the latest communication technology that uses optical fiber as the transmission medium to transmit information and achieve the purpose of communication.
The development process of communication is to continuously improvecarrier frequency In the process of expanding the communication capacity, the optical frequency, as the carrier frequency, has reached the upper limit of the communication carrier. Because light is an extremely high frequency electromagnetic wave, the communication capacity of using light as the carrier is huge, hundreds of times more than the past communication methods, which has great attraction. Optical communication is the goal that people have long pursued, and is also the inevitable direction of communication development.
Compared with the previous electrical communication, optical fiber communication has many advantages: its transmission frequency bandwidth and communication capacity are large;Low transmission loss and long relay distance;Fine wire diameter, light weight, raw material is quartz, which saves metal materials and is conducive to rational use of resources;insulationStrong anti electromagnetic interference performance;It also has the advantages of strong corrosion resistance, strong radiation resistance, good flexibility, no electric spark, small leakage, strong confidentiality, etcSpecial environmentOr military use.
trend
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5G network has a surge in demand for optical fiber and cable
The comprehensive construction of 5G network ushers in new opportunities for the development of the optical fiber market: 5G network needs a large number of base stations because the high-frequency signals it uses cannot cover a long distance;At the same time, optical fiber is the only material that provides the necessary high data transmission rate.Therefore, the demand for optical fiber in 5G networks will surge.[4]
