A. Wavelength division multiplexing (
WDM) and Dense Wavelength Division Multiplexing (DWDM) technology using wavelength division multiplexing device, a fiber Bu sent in multiple different wavelength optical carrier combiner, called wavelength division multiplexing . Use different wavelengths of light carrier not the transmission of different directions, can also achieve a single fiber bi-directional transmission. WDM capacity of two adjacent optical carrier wavelength interval between. Usually relatively large wavelength interval (50 - 100nm) system, known as the WDM system; wavelength interval is relatively small (10nm) system, known as dense wavelength division multiplexing (
DWDM) system; wavelength intervals of less than 1nm when , called optical frequency division multiplexing (FDM) system. WDM technology, the key is that the wavelength division multiplexing devices, namely sub-wave harmony wave. Their role in the transmission of different wavelengths in the light of the same system of photosynthetic Road to a fiber in the originator, the receiver will receive the optical signal is divided into different wavelengths of light signal to the optical detector, optical / electrical conversion.
Optical wavelength division multiplexing technology based on the business development needs on the basis of the existing fiber optic cable capacity expansion; WDM device with the direction of reversibility, ie, the same device can be used as a combiner and partial wave, so in a fiber bidirectional transmission can be achieved; wavelengths used in optical wavelength division multiplexing technology, modulation method, transmission rate, the type of the transmitted signal does not matter, but mutually compatible. WDM technology can increase the flexibility of the subscriber access network network. WDM technology in the development of high-speed broadband communications network will occupy an important position, it will promote the all-optical network to become a reality.
Two. Frequency division multiplexing (FDM) technology frequency division multiplexing and wavelength division multiplexing is essentially no difference between frequency and wavelength of the signal reciprocal relationship. Usually intervals of less than the wavelength of the optical carrier the 1nm system called optical frequency division multiplexing system. Similar to the optical wavelength division multiplexing system, the optical frequency division multiplexing, the key is frequency division multiplexer pieces. Very close to the wavelength interval of FDM, we must use high-resolution technology to select the signals of different wavelengths of light. Mainly in two ways: a tunable optical filter and coherent optical communication technology. FDM technology is mature, the reuse factor, has been widely used in the hybrid fiber / coax access network (HFC).
3. Space division multiplexing (SDM) empty-division multiplexing is the use of space (different lines) constitute a different channel transmission brightest light signal. For example, in the multi-core fiber optic cable to use different core fiber transmission signal of the signal transmission in different directions. Visible, proportional to the number of SDM, the capacity of the system and the cable core, so early in the optical access network construction, business capacity hours SDM technology that is simple and convenient way. Business capacity increases, additional capacity is needed, as long as the original cable line using appropriate optical multiplexing can achieve their goals.
4. Optical time division multiplexing (OTDM) technology is optical time division multiplexing is to make the brightest optical signal in the electrical / optical conversion at different times occupied by a single fiber transmission. OTDM technology, the key lies in the ultrashort pulse light source, optical modulators, optical time division multiplexing device, all-optical demultiplexer. OTDM technology enables the transmission of large capacity, transfer rate of up to hundreds of Gbit / s and 160Gbit / s such as NTT, Japan, 200kmOTDM optical soliton communication systems. OTDM and WDM technology wood combining can achieve higher capacity. But for now, when the light transmission rate is high, it is difficult to achieve accurate to the step of the sender and the receiver clock frequency and phase in optical access network OTDM communication system has not yet entered the practical stage. OTDM using a high-speed optical signal processing technology, easy to be compatible with future all-optical networks, so in the future the development of high-speed communications network, but also plays an important role.
5 carrier multiplexing (SCM) technology subcarrier multiplexing different roadbed charged signals to light after a battery carrier frequency division multiplexing (RF) modulation, both the power and then frequency division multiplexing signal the light-carrier light source is modulated and then transmitted through the optical fiber. Power frequency division multiplexing signal group at the receiving end, with after the optical / electrical conversion, recovery, and then through the electrolysis tone, restore the original roadbed live signal. First modulated electrical carrier is called a subcarrier. Subcarrier multiplexing the transmitted signals can be independent of each other independent of each other, and thus can achieve analog telephone, digital telephone, the image signal, and a variety of data services is compatible. Currently, SCM technology is used for CATV multi-channel transmission system users to access network. Optical fiber communication technology, with its characteristics of large capacity, high speed information transmission has been widely used. However, the transmission process of the signal to go through the conversion of multiple optical signals to electrical signals. As electronic devices there are bandwidth limitations, power loss, and vulnerable to electromagnetic interference and other shortcomings, so that the signal during transmission, the "electronic bottleneck" phenomenon, limiting the capacity of the system and further improve the rate. To this end, the people is studying the development is used to replace existing electrical light
