Optical communication (OpTIcal CommunicaTIon) is a communication method in which light waves are used as carriers. There are two ways to increase the optical path bandwidth: one is to increase the single-channel transmission rate of the optical fiber; the other is to increase the number of wavelengths transmitted in a single optical fiber, that is, wavelength division multiplexing (WDM).
Broadband Metropolitan Area Network (BMAN) is a hotspot of information construction in China. The huge bandwidth of DWDM (Dense Wavelength Division Multiplexing) and the transparency of transmitted data are undoubtedly the preferred technologies in today's optical fiber applications. However, MAN has the characteristics of short transmission distance, flexible topology and multiple access types. For example, DWDM, which is mainly used for long-distance transmission, is inevitably costly; at the same time, early DWDM is difficult to adapt to MAN and other flexible diversity. Faced with this low-cost metropolitan-wide broadband demand, CWDM (Coarse Wavelength Division Multiplexing) technology emerged as the times require, and soon became a practical device. For optical communications, its technology is basically mature, and business needs are relatively insufficient. Taking FTTH, which is known as the “final target of broadband accessâ€, as an example, its implementation technology EPON is fully mature, but the bandwidth required by ordinary users for Internet access is not high, so the commercial use of FTTH is limited to some pilot areas. However, in 2006, with the launch of triple play services such as IPTV, the bandwidth provided by operators could no longer meet the requirements of users for high-definition TV, and the deployment of FTTH was also put on the agenda. Coincidentally, ASON has flexible control over the transmission network and can provide personalized services for enterprise customers. Many operators develop and maintain enterprise customers, and they spare no expense to invest in building ASON.
The ultimate goal of the future transmission network is to build an all-optical network, that is, to achieve "optical fiber transmission instead of copper transmission" in the access network, metropolitan area network, and backbone network. The backbone network and the metropolitan area network have basically realized all-opticalization, and some areas of the network have developed rapidly, and some of the access layer's light enters and retreats.
Optical communication is a technique that uses light to transmit information to the other party.
Basic structure of optical communication
Computers and mobile phones around us send information via electrical signals "0 and 1". Optical communication is composed of a "transmitter" that converts an electrical signal into an optical signal, a "receiver" that converts an optical signal into an electrical signal, and a "fiber" that transmits light.
Advantages of optical communication
1. Long transmission distance, economical and energy saving
2. One-time transmission of massive information
3. Communication speed is fast
(1) Long transmission distance, economical and energy saving
Assume that 10Gb of information (10 billion signals) is transmitted in one second. If electrical communication is used, the signal is adjusted every 100 meters. In contrast, if optical communication is used, the adjustment interval needs to be 100 kilometers or more. The fewer the number of adjustment signals, the less the number of machines used, and therefore the economical and energy-saving effect.
For example, when talking to a foreign friend or chatting online, it feels no different from talking in the country. Unlike the past, the sound will lag behind. In the era of only electrical communication, the distance that can be transmitted at one time is short and the amount of information transmitted is small, and international communication is mainly transmitted as a relay through artificial satellites. However, when optical communication is used, the one-time transmission distance is long and the amount of information transmitted is large. Therefore, by using the optical fiber cable laid on the seabed, it is possible to realize natural communication with overseas. (The speed of the electric wave and the light are the same. However, since the transmission path becomes longer via the satellite, the signal arrives slowly. The distance of the submarine cable is much shorter, so the signal will be reached faster.)
(2) One-time transmission of massive information
A large number of users can receive the required information (movies or news, etc.) at the same time. In one second, electrical communication can only transmit up to 10Gb (10 billion 0 and 1 signals). In contrast, optical communication can transmit up to 1Tb (1 trillion 0 and 1 signals).
(3) Fast communication speed
The communication will be delayed due to electrical noise, resulting in a decrease in communication speed. However, optical communication is not affected by noise, so signals can be transmitted quickly.
Optical communication is communication in which light waves are used as carriers. There are two ways to increase the optical path bandwidth: one is to increase the single-channel transmission rate of the optical fiber; the other is to increase the number of wavelengths transmitted in a single optical fiber, that is, wavelength division multiplexing (WDM). In fact, optical communication equipment is only suitable for the last few The distance of kilometers is used.
The most basic fiber-optic communication system consists of a data source, an optical transmitter, an optical channel, and an optical receiver. The data source includes all signal sources, which are signals obtained by source coding of voice, image, data, etc.; the optical transmitter and modulator are responsible for converting the signal into an optical signal suitable for transmission on the optical fiber. The used lightwave windows are 0.85, 1.31, and 1.55. The optical channel includes the most basic fiber, and the relay amplifier EDFA, etc.; and the optical receiver receives the optical signal, extracts information therefrom, and then converts it into an electrical signal, and finally obtains corresponding information such as voice, image, and data.
Optical communication four technologies
Based on the above all-optical network architecture, there are many core technologies that will lead the future development of optical communications. The following focuses on the four most important technologies of ASON, FTTH, DWM, and RPR.
(1) ASON
Regardless of the progress of domestic R&D, trial commercialization, or development experience from abroad, it is an inevitable trend for domestic operators to introduce ASON technology on a large scale in the transmission network. ASON (AutomaTIcally Switched Optical Network) is an optical transport network technology. The current product and market conditions indicate that ASON technology has reached commercial maturity. With the large-scale deployment of 3G and NGN, business demand will further drive the development of transport network technology. It is expected that ASON will be more widely commercialized in 2007.
In 2006, major equipment suppliers such as Huawei, ZTE, Fiberhome, and Lucent have launched their commercial ASON products. China Telecom, China Netcom, China Mobile, China Unicom and China Railcom have successively launched ASON application testing and small-scale commercial use.
ASON's successful commercial experience abroad shows that ASON will play an irreplaceable role in the backbone transmission network. For example, AT&T's 140 nodes cover the US backbone transport network; BT sets up 21CN network, currently has 40 ASON nodes; Vodafone's 131 nodes cover the UK's ASON backbone transport network, and so on.
However, at present, the standardization work of ASON in routing, automatic discovery, ENNI interface, etc. is still not perfect, which has become an important factor restricting the development and commercialization of ASON technology. In the future, China will participate in more ASON standardization work. At the same time, the standardization of ASON, especially the standardization of ENNI, will make breakthrough progress in recent years.
(2) FTTH
FTTH (Fiber To The Home) is the ultimate goal of next-generation broadband access. At present, in the technology of implementing FTTH, EPON will become the mainstream technology in China in the future, and GPON has the most development potential.
EPON adopts Ethernet encapsulation, so it is very suitable for carrying IP services, which is in line with the rapid development of IP networks. At present, the country has taken EPON as a major project of the “863†program and has taken the initiative in commercial operation.
GPON is more focused on multi-service support than EPON, so it is more suitable for the future development of converged networks and converged services. However, it is still not mature enough and the price is too high to be widely promoted in China.
China's FTTH is still in the market start-up phase, and there is still a long way to go from large-scale commercial deployment. In the future industrialization development, the operator's monopoly on the “last mile†of the local network is an important factor restricting the development of FTTH. It takes the form of “customer network operator and real estate developer to cooperateâ€, which is more conducive to FTTH industry. Healthy development. From the experience of FTTH development in Japan, the United States, Europe and South Korea, the core driving force of FTTH lies in the rich content provided by the network, and the government's monitoring and management policies on applications and content will also restrict the development of FTTH.
(3) WDM
WDM breaks through the limits of traditional SDH network capacity and will become the core transmission technology of future optical networks.
According to the channel spacing, WDM (Wavelength Division Multiplexing) can be divided into two technologies: DWDM (Dense Wavelength Division Multiplexing) and CWDM (Sparse Wavelength Division Multiplexing). DWDM is the technology of choice in today's fiber-optic transmission field, but CWDM also has its place.
In 2006, equipment manufacturers such as FiberHome and Huawei launched their own DWDM systems, and domestic operators also carried out related tests and small-scale commercial use. In the future, DWDM will play an irreplaceable role in networks with demanding transmission rates, such as using DWDM to build backbone networks.
Compared with DWDM, CWDM has the advantages of low cost, low power consumption, small size, and low requirements on optical fibers. In the next few years, telecom operators will strictly control network construction costs. At this time, CWDM technology has its own living space. It is suitable for fast, low-cost multi-service network construction, such as metropolitan area and local access network, small and medium-sized enterprises. The city's metro core network, etc.
(4) RPR
Resilient Packet Ring (RPR) will become an important optical metropolitan area network technology in the future. In recent years, many domestic and foreign transmission equipment manufacturers have developed MSTP equipment with embedded RPR function. RPR technology has received support and participation from a large number of chip manufacturers, equipment manufacturers and operators.
In terms of standardization, the IEEE 802.17 RPR standard has been recognized by the entire industry, and domestic related standardization work is still in progress. In the future, RPR will be mainly applied to the backbone and access of metropolitan area networks. It can also be applied in decentralized government networks, enterprise networks and campus networks, and can also be applied to IDCs and ISPs.
Optical communication advantages
Optical fiber communication has received great attention because of its unparalleled superiority compared to other communication methods.
(1) Large communication capacity
In theory, an optical fiber with only the thickness of the hair can transmit 100 billion words at the same time. Although it is far from reaching such a high transmission capacity, the experiment of transmitting 240,000 voice channels simultaneously with one optical fiber has been successful, and it is several tens or even thousands higher than the conventional bright wire, coaxial cable, microwave, etc. More than double. The transmission capacity of a fiber is so huge, and a fiber optic cable can include dozens or even thousands of fibers. If wavelength division multiplexing is used to treat one fiber as several or dozens of fibers, The communication capacity is even more amazing.
(2) Long relay distance
Because the fiber has a very low attenuation coefficient (currently commercialized quartz fiber has reached 0.19dB/km or less), it can be relayed for hundreds of kilometers or more with appropriate optical transmission and light receiving equipment. This is a traditional cable (1.5km), microwave (50km) and so on can not be compared. Therefore, optical fiber communication is especially suitable for long-distance primary and secondary trunk communication. It has been reported that the use of an optical fiber to simultaneously transmit 240,000 voice channels and 100 km without relay has been successful. In addition, the optical soliton communication test that has been carried out has reached a level of 1.2 million voice channels and 6000 km without relay. Therefore, it is entirely possible to realize global unrelayed fiber-optic communication in the near future.
(3) Good confidentiality
When the light wave is transmitted in the optical fiber only in its core region, basically no light "leaks out", so its security performance is excellent.
(4) Strong adaptability
It means that it is not afraid of interference from external strong electromagnetic fields, corrosion resistance, and strong flexibility (the performance is not affected when the bending radius is greater than 25 cm).
(5) Small size and light weight
Easy construction and maintenance, easy to construct and maintain, easy to construct and maintain, easy to construct and maintain. The laying method of the optical cable is convenient and flexible, and can be directly buried, pipe laid, underwater and overhead.
(6) Rich source of raw materials, low potential price
The most basic raw material for making quartz fiber is silicon dioxide, sand, which is almost inexhaustible in nature. Therefore its potential price is very low.
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