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.
Principle of 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.
The birth and development of optical fiber communication is a major revolution in the history of telecommunications, which ranks alongside satellite communication and mobile communication as technologies in the 1990s. After entering the 2 1 century, due to the rapid development of internet services and the growth of audio, video, data and multimedia applications, the demand for large-capacity (ultra-high-speed, ultra-long distance) optical wave transmission systems and networks is more urgent.
Optical fiber communication is a new communication technology which uses light wave as the carrier and optical fiber as the transmission medium to realize information transmission and achieve communication purposes.
The development of communication is a process of expanding communication capacity by constantly improving carrier frequency. As a carrier frequency, optical frequency has reached the upper limit of communication carrier. Because light is an electromagnetic wave with a very high frequency, it has a huge communication capacity, which is thousands of times that of the past communication methods and has great attraction. Optical communication is the long-term goal of people and the inevitable direction of communication development.
Compared with the previous electric communication, optical fiber communication has many advantages: wide transmission frequency bandwidth and large communication capacity; Low transmission loss and long relay distance; Thin wire diameter, light weight, timely raw materials, saving metal materials, and being beneficial to the rational utilization of resources; Strong insulation and anti-electromagnetic interference ability; It also has the advantages of strong corrosion resistance, strong radiation resistance, good winding, no electric spark, small leakage and strong confidentiality, and can be used in special environments or military affairs.
Optical fiber communication has a wide range of applications, mainly for local telephone trunk lines. The advantages of optical fiber communication can be brought into full play here, gradually replacing cables and being widely used. It is also used for long-distance trunk communication. In the past, it mainly relied on cable, microwave and satellite communication, but now it gradually uses optical fiber communication, forming a global dominant bit transmission mode. Used in global communication networks and national public telecommunication networks (such as China's national first-class trunk lines, provincial second-class trunk lines and branch lines below the county level); It is also used in high-quality color TV transmission, industrial production site monitoring and dispatching, traffic monitoring and command, urban cable TV network, antenna (CATV) system, optical fiber local area network and other applications, such as airplanes, spacecraft, ships, underground mines, electric power departments, military and corrosive and radioactive.
Optical fiber transmission system is mainly composed of optical transmitter, optical receiver, optical cable transmission line, optical repeater and various passive optical devices. In order to realize communication, the baseband signal must be processed by the electrical terminal and sent to the optical fiber transmission system to complete the communication process.
It is suitable for optical fiber analog communication system, optical fiber digital communication system and data communication system. In optical fiber analog communication system, electrical signal processing refers to baseband signal amplification and pre-modulation. And the inverse processing of electric signal is the inverse process of initial processing, that is, demodulation, amplification and other processing. In optical fiber digital communication system, electrical signal processing refers to the amplification, sampling and quantization of baseband signals, that is, pulse code modulation and line coding processing. And the reverse processing of electrical signals is also the reverse process of the originator. For data optical fiber communication, electrical signal processing mainly includes signal amplification, which is different from digital communication system in that there is no need for coding conversion.
How to develop optical fiber communication technology in the future?
Recently, some people are very confused about the development of optical fiber communication. First, in 2000, the bubble in the IT industry led to excessive investment and overproduction in the production scale of optical fiber communication, and many small companies in the IT industry closed down. Especially optical fiber, are dumped to China by foreign countries. Secondly, some people think that the transmission capacity of optical fiber communication has reached 10Tbps, which is almost inexhaustible, and now all major trunk lines are almost built, and there are many remaining optical fibers buried underground, so optical fiber communication technology does not need more development.
Development trend of optical fiber communication
1, FTTH development
FTTH can provide users with extremely rich bandwidth, so it has always been regarded as an ideal access mode, which plays an important role in realizing the information society and needs to be popularized and built on a large scale. The number of optical fibers needed by FTTH may be 2 ~ 3 times that of existing coated optical fibers. In the past, due to the high cost of FTTH and the lack of broadband video service and broadband content, FTTH has not been put on the agenda, and there are only a few experiments. Recently, due to the progress of photoelectric devices, the prices of optical transceiver modules and optical fibers have been greatly reduced; Coupled with the looseness of broadband content, the practical process of FTTH is accelerated.
Developed countries have different views on FTTH: American AT & amp； T thinks that the FTTH market is very small, and in June 2003, he declared that FTTH will have a market in 20-50 years. American operators Verizon and Sprint are more active in adopting FTTH for network transformation within 10- 12 years. Japan's NTT first developed FTTH, and now it has nearly 2 million users. At present, FTTH in China is in the pilot stage.
◆FTTH [Challenge: ADSL technology, which is widely used now, still has certain advantages in providing broadband services.
Compared with FTTH, it is cheaper, and the original copper network is used to make the project construction simple. At present, the transmission of 1 Mbps-500 kbps video programs can meet the demand. At present, the large-scale promotion of FTTH is restricted.
AD8L is difficult to meet the broadband services to be developed in the near future, such as two-way services such as online education, online office, conference TV, online games, remote diagnosis and treatment, and services with asymmetric uplink and downlink transmission of HDTV. Especially for HDTV, its transmission rate still needs 19.2Mbps after compression, and it is being developed with H.264 technology, which can be compressed to 5 ~ 6mbps. It is generally believed that the highest transmission speed string of ADSL with guaranteed QOS is 2Mbps, so it is still difficult to transmit HDTV. It can be considered that HDTV is the main driving force of FTTH. That is to say, FTTH is necessary when HDTV service comes.
◆ FTTH solutions: There are usually two types: P2P peer-to-peer and PON passive optical networks.
Advantages of F2P scheme: each user transmits independently, without affecting each other, and the system changes flexibly; Cheap low-speed photoelectric modules can be used; Long transmission distance. Disadvantages: In order to reduce the number of optical fibers and pipes for users to go directly to the office, it is necessary to install 1 active nodes for summarizing users in the user area.
PON scheme-Advantages: simple maintenance of passive network; In principle, photoelectric devices and optical fibers can be omitted. Disadvantages: expensive high-speed photoelectric modules are needed; It is necessary to use electronic modules with different distances to distinguish users and avoid the collision of users' uplink signals; Transmission distance is shortened due to PON ratio; The downlink bandwidth of each user occupies each other. If the user bandwidth cannot be guaranteed, it is necessary not only to expand the network, but also to replace the PON and user modules. According to the current market price, PEP is more economical than PON.
There are many kinds of PON, generally as follows: (1)APON: ATM-PON, which is suitable for ATM switching networks. (2)BPON: broadband PON. (3)OPON: OFP-PON for general frame processing. (4)PON, 0EPON adopts Ethernet technology, and 0 EPON is a Gigabit Ethernet PON. (5)WDM-PON: Wavelength division multiplexing (WDM) is used to distinguish the PON of users. Because the user is related to the wavelength, it is inconvenient to maintain, so it is rarely used in FTTH.
The plans and technical schemes of FTTH development in developed countries are different according to the specific conditions of each country. A-PON is mainly used in the United States because ATM switching is widely used in the United States. Japan's NTT has a B-FLETts plan, which adopts P2P-MC, B-PON, G-EPON, SCM-PON and other technologies. SCM-PON: It is a kind of PON that uses subcarrier modulation as multiplexing.
The use of ATM in China is far less than SDH in STM, so APON is generally not considered. We can consider P2P, GPON and EPON. The advantages and disadvantages of P2P scheme have been mentioned before. At present, it is economical, flexible to use and long in transmission distance. Proper use. Comparing GPON and EPON has its own advantages and disadvantages. GPON: Using GFP technology, the network efficiency is high; Can have a telephone, suitable for SDH network. The combination with IP is not as good as EPON, but GPON technology is not mature at present. EPON: It is well integrated with IP. Users can use lAD technology if they want to use their mobile phones. At present, EPON has been widely used in FTTH pilot project in China. The adoption of FTTH technical scheme also needs to be different according to the specific situation of users.
In recent years, wireless access technology has developed rapidly. IEEE802. 1 1g protocol, which can be used as WLAN, has a transmission bandwidth of 54Mbps and a coverage of over 100 meters, and has been commercialized. If wireless access to WLAN is used for data transmission of users, including uplink and downlink data of VOD, the uplink is not large for ordinary users, and IEEE 02. 1 1G+0G can meet it. FTTH using optical fiber mainly solves the downlink transmission of broadband video of HDTV, and of course, it can also contain some downlink data when necessary. This forms a "FTTH+ wireless access" home network. This home network is particularly simple if it adopts PON, because there is no uplink signal in this PON and no ranging electronic module is needed, so the cost is greatly reduced and the maintenance is simple. If the user group of the PON is covered by WiMAX (1 EEE802.5438+06) and can be used, it is not necessary to establish a dedicated WLAN. It is a trend to adopt wireless access network, but wireless access network still needs optical fiber network close to users to support, which is similar to FTTH. FTTH+ wireless access is the future development trend.
2. The development of optical switching What is communication?
In fact, it can be expressed as: AC input+communication.
Optical fiber only solves the problem of transmission, but also needs to solve the problem of optical switching. In the past, communication networks used metal cables to transmit electronic signals and exchange them with electronic switches. Now, except for a short section of the client, the communication network is all optical fiber, transmitting optical signals. The reasonable method should adopt optical switching. However, at present, due to the immaturity of optical switching devices, only the "optical-electrical-optical" mode can be used to solve optical network switching, that is, optical signals are converted into electrical signals, and then converted into optical signals through electronic switching. Obviously it is unreasonable, inefficient and uneconomical. Large-capacity optical switches are being developed to realize optical switching networks, especially ASON automatic switching optical networks.
Usually, the speed of information transmission in optical networks is xGbps, and electronic switches are not competent. General electronic exchange should be realized in low-order groups. Optical switching can realize high-speed XGbDs switching. Of course, it doesn't mean that everything depends on light to exchange, especially the signal exchange of low-speed small particles. Mature electronic exchanges should be used, and there is no need to use immature ones.
Large capacity optical switching. At present, in the data network, signals appear in the form of "packets", which is called "packet switching". The particles in the bag are relatively small and can be exchanged electronically. However, after a large number of groups in the same direction are summarized, when the number is large, large-capacity optical switching should be adopted.
At present, optical switching with few channels and large capacity has been put into practical use. For example, it is used for protection, downlink and few path scheduling. It is generally realized by mechanical optical switch and thermo-optical switch. At present, due to the limitation of volume, power consumption and integration, the number of paths of these optical switches is generally 8- 16.
Electronic exchange generally has two modes: "space division" and "time division". Optical switching includes "space division", "time division" and "wavelength switching". Optical time division switching is rarely used in optical fiber communication.
Optical spatial switching: In general, optical switches can be used to transmit optical signals from one optical fiber to another. Optical switches in air separation include mechanical, semiconductor and thermo-optical switches. Recently, MEMS micro-motor optical switch has been developed by using integrated technology, and its size is as small as mm. The 1296x 1296MEM optical switch (Lucent) has been developed, which is experimental.
Optical wavelength exchange: it is to assign 1 specific wavelength to each exchange object. Therefore, you can send a wavelength of 1 to communicate with an object. The key to realize optical wavelength exchange is to develop practical variable wavelength light source, optical filter and integrated low power and reliable optical switch array. A 640x640 semiconductor optical switch +AWG cross-connection test system (Corning Company) was developed. A very flexible optical switching network can be constructed by using optical spatial division and optical wavelength division. NTT of Japan conducted a field test of wavelength routing switching in Chitose City, with a radius of 5 km, * * * 43 terminal nodes (5 nodes were tried out) and a speed of 2.5Gbps.
Automatic switched optical network called ASON is the direction of further development.
3. Development of integrated optoelectronic devices
Photoelectric devices, like electronic devices, should be integrated. Although not all optoelectronic devices need to be integrated, a considerable number of them are needed and can be integrated. The PLC- planar optical waveguide circuit being developed at present, like printed circuit board, can be assembled with photoelectric devices or directly integrated into a photoelectric device. In order to realize FTTH or ASON, new, small, cheap and integrated optoelectronic devices are needed.
NTT in Japan developed 16x 16 thermo-optical switch by PLO technology. 1x 128 thermo-optical switch array; 32-channel AWG+ variable optical attenuator+optical power monitoring is integrated by integration and hybrid integration technology; Multiplexing and demultiplexing of WDM with 8 wavelengths and 80Gbps wave speed string are integrated on 1 chip, and the size is only 15x7mm, as shown in figure 1. NTT uses the above integrated devices to form a 32-channel OADM. Some of them have been commercialized. In recent years, integrated optoelectronic devices have been greatly improved.
China's integrated optoelectronic devices have also made some progress. The integrated small channel optical switch and AWG belonging to PLO technology have made a breakthrough. But there is still a big gap with developed countries. If we don't catch up, we will repeat the passive situation of microelectronics backwardness.
Optical fiber communication market
As we all know, the IT industry bubble in 2000 made the production scale of optical fiber communication industry explode, leading to overproduction of products. The prices of optical transmission equipment, photoelectric devices and optical fibers plummeted. Especially optical fiber, the price per kilometer in the bubble period was 1200, and now the price is about 100, which is cheaper than copper wire. When will the optical fiber communication market recover?
According to the statistics and forecast of RHK's investment in North American communication industry, as shown in Figure 2, 2002 is the lowest point, which is equivalent to a retrogression of four years. Now it has picked up, but it can't be recovered yet. According to this speculation, it will recover in 2007-2008. The optical fiber communication market also develops with the development of IT market. These improvements are largely driven by FTTH and broadband digital TV.
FTTH is, after all, the demand of the information society, and the market of optical fiber communication must have a beautiful scene. FTTH has been built in developed countries and has a considerable market. Generally speaking, with the market demand, the profits of devices and equipment will gradually pick up and 2007-2008 may be good. However, despite the success of anti-dumping, the price of optical fiber industry is still very low and the profit is very small. In fact, worldwide, the production scale of optical fiber is too large, and the development speed of FTTH is affected by the social environment, including the economic conditions of citizens and the development of digital TV, and it rises slowly. It is understood that some large companies have closed several optical fiber factories and can start production at any time according to market conditions. As a result, supply always exceeds demand. The general law of the market is that the price can only be raised if the supply exceeds the demand, so it may be after 2009 if the optical fiber industry wants to make a big profit. The underdeveloped areas and small towns in China still need to build optical fiber lines, but the amount of optical fiber is still within the demand range of Prince.
For China market, FTTH will be delayed due to the challenge of ADSL and the limitation of HDTV development. At present, the social environment and conditions for building FTTH in China are not yet available, and it may take some time. However, the Beijing Olympic Games needs the promotion of HDTV and the decrease of equipment price, which will promote the development of FTTH. It is expected to be popularized in FTTH, China in 2007-2008. But in some big cities, there are also so-called Central Business District (CBD), which has relatively strong economic strength, and now PTTP is used to build it. Generally speaking, FTTH in China is in the pilot stage. The role of the pilot, on the one hand, is to explore the experience of technology and construction, on the other hand, it also plays the role of competition to seize users. Therefore, telecom operators and local owners are actively piloting FTTH to develop broadband services. Therefore, broadcasters are facing great challenges. Broadcasting companies should speed up the development of digital TV, enrich the program content and adopt a competitive business model. If broadcasters want to develop VOP on demand TV, they need to transform the cable TV network in both directions. If the optical fiber network is adopted, it can fully adapt to the future technical development and market demand.