Optical communication (OpTical CommunicaTion) is a communication method using light waves as a carrier. There are two ways to increase the bandwidth of the optical path: one is to increase the single-channel transmission rate of the fiber; the other is to increase the number of wavelengths transmitted in a single fiber, that is, wavelength division multiplexing (WDM).
Broadband Metropolitan Area Network (BMAN) is a hotspot in information construction. DWDM (Dense Wavelength Division Multiplexing) has huge bandwidth and transparency of data transmission, and is undoubtedly the preferred technology in today's optical fiber application field. However, MAN has the characteristics of short transmission distance, flexible topology and multiple access types. For example, copying DWDM, which is mainly used for long-distance transmission, will inevitably cost too much. At the same time, early DWDM is also difficult to adapt to the flexibility and diversity of MAN. Faced with this low-cost metropolitan area wideband demand, CWDM (Coarse Wavelength Division Multiplexing) technology emerged as the times require, and soon became a practical device.
For optical communication, its technology is basically mature, but the business demand is relatively insufficient. Take FTTH, which is known as "the ultimate goal of broadband access," as an example. Its implementation technology, EPON, is fully mature. However, because the bandwidth required by ordinary users to access the Internet is not high, the commercialization of FTTH is accelerated.
The ultimate goal of the future transmission network is to build an all-optical network, that is, to fully realize "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 achieved all-opticalization, and some areas where the network develops rapidly have also realized the optical advance and copper retreat of part of the access layer.
Optical communication is a technology that uses light to transmit information to each other.
Optical Communication Structure Principle
The basic structure of optical communication
Computers and mobile phones around us send information through electrical signals "0 and 1". Optical communication consists of a "transmitter" that converts electrical signals into optical signals, a "receiver" that converts optical signals into electrical signals, and a circuit "optical fiber" that transmits light.
Advantages of Optical Communication
1. Long transmission distance, economical and energy saving
2. One-time transmission of massive information
3. Fast communication speed
(1) Long transmission distance, economical and energy saving
Assuming that 10 Gb of information (10 billion signals) is to be transmitted in 1 second, if electrical communication is used, the signal must be adjusted every 100 meters. On the other hand, if optical communication is used, the interval that needs to be adjusted can be 100 kilometers or more. The fewer times the signal is adjusted, the fewer machines are used, so it has the effect of economical and energy saving.
For example, when talking with friends abroad or chatting on the Internet, it feels no different from calling in China. The sound doesn't lag like it used to. 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 through artificial satellites as relays. However, with optical communication, the transmission distance is long and the amount of information transmitted at one time is large. Therefore, by using optical fiber cables laid on the seabed, natural and smooth communication with overseas countries can be realized. (The speed of radio waves is the same as that of light. However, since the transmission path through the satellite becomes longer, the signal arrives slower. The distance of the submarine cable is much shorter, so the signal arrives faster.)
(2) One-time transmission of massive information
A large number of users can simultaneously receive desired information (movies or news, etc.). In 1 second, electrical communication can only transmit a maximum of 10Gb (10 billion 0s and 1s) of information, compared to optical communication that can transmit a maximum of 1Tb (1 trillion 0s and 1s).
(3) Fast communication speed
In electrical communication, errors can occur 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 using light waves as carrier waves. There are two ways to increase the bandwidth of the optical path: one is to increase the single-channel transmission rate of the fiber; the other is to increase the number of wavelengths transmitted in a single fiber, namely wavelength division multiplexing (WDM). In fact, optical communication equipment is only suitable for the last few days. distance in kilometers.
The most basic optical fiber 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 the signals obtained by encoding the voice, image, data and other services through the source; the optical transmitter and the modulator are responsible for converting the signal into an optical signal suitable for transmission on the optical fiber, successively The used lightwave windows are 0.85, 1.31 and 1.55. The optical channel includes the most basic optical fiber, as well as the relay amplifier EDFA, etc.; and the optical receiver receives the optical signal, extracts information from it, and then converts it into an electrical signal, and finally obtains the corresponding voice, image, data and other information.
Four technologies of optical communication
Based on the above-mentioned all-optical network architecture, there are many core technologies, which will lead the future development of optical communication. The following focuses on introducing the four most important technologies of ASON, FTTH, DWM and RPR.
FTTH
FTTH (Fiber To The Home) is the ultimate goal of broadband access. At present, among the technologies for realizing FTTH, EPON will become the mainstream technology in the future, and GPON has the most development potential.
EPON adopts the Ethernet encapsulation method, so it is very suitable for carrying IP services, which is in line with the trend of rapid development of IP networks. At present, EPON has taken the initiative in commercial operation.
GPON pays more attention to the support capability of multi-service than EPON, so it is more suitable for the development of converged network and converged services in the future.
FTTH is still in the market launch stage, and it is still some distance away 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. Adopting the form of "cooperation between customer premises network operators and real estate developers" is more conducive to the FTTH industry. healthy development. Judging from the FTTH development experience in countries such as 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 for applications and content will also restrict the development of FTTH.
Advantages of Optical Communication
The reason why people attach great importance to optical fiber communication is that it has unparalleled superiority compared with other communication means.
(1) Large communication capacity
In theory, an optical fiber as thin as a human hair can transmit 100 billion channels at the same time. Although it is far from reaching such a high transmission capacity at present, the experiment of transmitting 240,000 voice channels at the same time with one optical fiber has been successful, which is tens or even thousands higher than the traditional open wire, coaxial cable, microwave, etc. times more. The transmission capacity of an optical fiber is so huge, and an optical cable can include dozens or even thousands of optical fibers. If the wavelength division multiplexing technology is used to use one optical fiber as several or dozens of optical fibers, its The communication capacity is even more astonishing.
(2) Long relay distance
Because the optical fiber has a very low attenuation coefficient (the current commercial silica fiber has reached below 0.19dB/km), if it is matched with appropriate optical transmitting and optical receiving equipment, the relay distance can reach more than hundreds of kilometers. This is incomparable with traditional cables (1.5km), microwaves (50km), etc. Therefore, optical fiber communication is especially suitable for long-distance primary and secondary trunk communication. According to reports, the experiment of transmitting 240,000 voice channels at the same time with one optical fiber and 100 kilometers without repeaters has been successful. In addition, the optical soliton communication test that has been carried out has reached the level of transmitting 1.2 million voice channels and 6,000 kilometers without repeaters. Therefore, it is entirely possible to realize global optical fiber communication without relays in the near future.
(3) Good confidentiality performance
When the light wave is transmitted in the fiber, it is only carried out in its core area, and basically no light "leaks" out, so its security performance is excellent.
(4) Strong adaptability
It means that it is not afraid of the interference of strong external electromagnetic fields, has corrosion resistance, and has strong flexibility (its performance will not be affected when the bending radius is greater than 25 cm).
(5) Small size and light weight
Ease of construction and maintenance Ease of construction and maintenance Ease of construction and maintenance Ease of construction and maintenance. The laying method of optical cable is convenient and flexible, which can be directly buried, pipeline laying, underwater and overhead.
(6) Abundant sources of raw materials and potential low prices
The most basic raw material for making silica fiber is silica, that is, sand, and sand is almost inexhaustible in nature. Therefore, its potential price is very low.
