Traditional transmission network expansion methods use space division multiplexing (SDM) or time division multiplexing (TDM). The basic transmission network of Space-division multiplexing(SDM) and time-division multiplexing expansion(TDM) uses PDH or SDH technology transmitted by a single wavelength optical signal. Since the bandwidth of an optical fiber is infinite, the SDM and TDM methods cause a huge waste of optical fiber bandwidth resources. Under such circumstances, Dense Wavelength Division Multiplexing (DWDM) technology has been generated, which greatly increases the capacity of the network and makes full use of the bandwidth resources of the fiber. With the rapid development of optoelectronic devices, especially the maturity and commercialization of EDFA, the dense wavelength division multiplexing technology has been widely used.
The Technology of Dense Wavelength Division Multiplexing (DWDM)
Wavelength division multiplexing (DWDM) is a series of optical carriers carrying information at a wavelength interval of 1 to several hundred nanometers in the optical frequency domain. At the transmitting end, they are multiplexed and coupled together along a single fiber transmission. At the receiving end, the technology of demultiplexing optical carriers of different wavelengths through a demultiplexer. Because the optical signals of each different wavelength channel are transmitted independently in the same fiber, multiple types of information (such as sound, data, and images) can be transmitted in one fiber core. It can make full use of the transmission characteristics of optical fiber broadband, so that one optical fiber plays the role of multiple optical fibers.
The Application of Dense Wavelength Division Multiplexing (DWDM)
DWDM(Dense Wavelength Division Multiplexing) system has the characteristics of large transmission capacity, long transmission distance and high price. So it is widely used in national trunk lines, provincial trunk lines, and metro core transmission systems. In long-distance transmission, the DWDM system uses NZDSF fiber (non-zero dispersion-shifted fiber), high-wavelength stability laser, dense wavelength division multiplexer and demultiplexer to perform optical power equalization on the entire line. In addition, DWDM systems have relatively complete protection methods and network management.
The DWDM system networking is generally a ring network topology. The nodes use optical protection Optical add-drop multiplexing(OADM)equipment, and use optical multiplex segment protection and optical channel protection ring systems. All are protected, which greatly improves system reliability. Operators in some large cities tend to choose high-reliability DWDM systems at the core layer of the metropolitan area in order to solve the problem of tight bandwidth resources and ensure system reliability.
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