Wavelength division multiplexing (WDM) is to two or more different wavelengths of light carrier signal () carry a variety of information in the sending end by Multiplexer (also called filter, Multiplexer) join together, and coupled to the same root of light in optical fiber transmission technology; At the receiving end, the solution of multiplexer (also called partial wave or Demultiplexer and Demultiplexer) separate the various wavelengths of light carrier, and then by the optical receiver to restore the original signal for further processing. This transfer both in the same optical fibers or numerous technology of different wavelengths of light signals, called WDM.
WDM wavelength division system is essentially a light frequency division multiplexing FDM technology domain. Each wavelength channel by division of frequency domain implementation, each wavelength channel occupies a bandwidth of optical fiber. WDM system adopts the wavelength is different, which is a specific wavelength standard, in order to distinguish it from ordinary wavelength SDH system, sometimes called color optical interface, and call the light of the common optical system interface "white mouth" or "white".
Communication system design is different, each has a different wavelength interval between width. Depending on the channel spacing, WDM can be subdivided into CWDM (sparse wavelength division multiplexing) and DWDM (DWDM). CWDM channel spacing is 20 nm, and the channel interval DWDM from 0.2 nm to 1.2 nm, so relative to the DWDM, CWDM called sparse wavelength division multiplexing technology.
due to the reuse of WDM system can light path rate of 2.5 Gbit/s, 10 Gbit/s, etc., and the number of multiplexing optical path can be 4, 8, 16, 32, or more, so the system transmission capacity can reach 300-400 - Gbit/s, is even greater.
1 for single wavelength system, SDH system requires a pair of optical fiber; And for WDM system, no matter how many SDH subsystem, the reuse system only need a pair of optical fiber. For example, for 16 2.5 Gbit/s system, single wavelength system need 32 optical fiber, and WDM system only need two optical fibers.
As long as to increase the number of multiplexing channel and devices can increase system in order to realize the expansion of transmission capacity, multiplexing channel WDM system is independent of each other, so each channel can transmit signals of different business, transparently, respectively, such as voice, data and images, each other noninterference, it brings great convenience to users.
EDFA has the advantages of high gain, wide bandwidth, low noise, and the light amplification range of 1530-1565 nm, but the gain curve of the flat part is 1540 (1560 nm), it can cover almost WDM system of 1550 - nm wavelength range. So in a very wide bandwidth of EDFA can reuse of WDM system light pathways for the amplified signal at the same time, in order to realize long distance transmission system, and to avoid the every optical transmission system needs a light amplifier. WDM system of long transmission distance up to hundreds of kilometers and save a lot of relay device, reduce the cost.
Because most of the WDM systems is a photoelectric device and photoelectric device reliability is high, so the system reliability can be guaranteed.
All optical network is the development direction of future optical transport network. In all-optical networks, all kinds of business, such as cross connection is up and down on the way light through the optical signal scheduling, thereby eliminating the bottleneck of the electronic device in the E/O conversion. WDM system can be used mixed with high speed, propsed, to form with high flexibility, high reliability, high survivability of all-optical network, to adapt to the development of transport network bandwidth needs.
A key advantage of DWDM is its protocol and transmission speed is not relevant. Based on DWDM network can use IP and ATM, SONET/SDH and Ethernet protocol to transmit data, processing data flow in the 100 Mb/s and 2.5 Gb/s, so, based on DWDM networks can be on a laser channel in different speeds of different types of data traffic. From point of view, the QoS (quality of service) based on DWDM network with a low cost way to quickly respond to changing customer's bandwidth requirements and agreement. Science and technology in the increasingly update, in national trunk, trunk lines provincial and municipal trunk with 1600 g, 800 g and 400 g also abound. Take 1600 g for example: in theory, under the condition of the cable have completely, a single fiber can go 160 article 10 g. Greatly improve the utilization rate of the fiber. Is also high to the requirement of fiber optic cable, of course, the theoretical value and actual value is biased, in order to avoid the failure rate in practical application are rarely on the same optical fibers with hundreds of business of channel.