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DWDM Definition And Working Method

DWDM is capable of combining and transmitting different wavelengths simultaneously in the same fiber. To be effective, one fiber is converted into multiple virtual fibers. So, if you plan to reuse 8 fiber carriers (OCs), that is, 8 signals in one fiber, the transmission capacity will increase from 2.5Gb/s to 20Gb/s. Data was collected in March 2013. Due to the adoption of DWDM technology, a single fiber can transmit more than 150 beams of different wavelengths simultaneously, and the maximum speed of each beam can reach 10Gb/s. As vendors add more channels to each fiber, terabits per second is just around the corner.


A key advantage of DWDM is that its protocol and transmission speed are irrelevant. The DWDM-based network can transmit data using IP protocol, ATM, SONET/SDH, and Ethernet protocols, and the processed data traffic is between 100 Mb/s and 2.5 Gb/s. In this way, a DWDM-based network can transmit different types of data traffic at different speeds on a single laser channel. From a QoS (Quality Service) perspective, DWDM-based networks respond quickly to customer bandwidth requirements and protocol changes in a cost-effective manner.

The relationship between communication transmission networks and services has become increasingly complex in the context of a rapidly rising traffic volume. The original TDM (fiber single-wave transmission and time-division multiplexing) cannot meet the needs of new technologies. Fiber optic single-wave transmission commercial applications have a maximum rate of 40 Gbits/s and are expensive. TDM technology is difficult to adapt to complex network and business relationships. The optical fiber multi-wave transmission technology using long-wave scheduling using pure optical devices breaks the limit of processing speed of electronic devices. On the basis of SDH technology, the optical fiber transmission capacity can be greatly improved. The current commercial application rate of dense optical wavelength multiplexing (DWDM) technology (DWDM) technology (also known as OTN technology) has reached 3.2 Tbits/s, which means that the communication network can be smoothly upgraded and evolved. 

The first proposed party for DWDM technology is Lucent, whose Chinese translation is dense optical multiplexing. DWDM technology was introduced in 1991. Specifically, it can combine a set of optical wavelengths and transmit them by one fiber. This is a laser technology used to increase the bandwidth on the existing fiber backbone. It can also be referred to multiplexing the tight spectral spacing of individual fiber carriers in a particular fiber to achieve the required performance during transmission. And you can try to reduce the number of fibers you need under a certain amount of information transmission. In recent years, the development of DWDM technology has received extensive attention, and DWDM technology will be more widely used in communication in the future. 


DWDM technology utilizes the bandwidth and low loss characteristics of single-mode fiber, and uses multiple wavelengths as carriers to allow each carrier channel to transmit simultaneously in the fiber.


Compared with the general single-channel system, dense WDM (DWDM) not only greatly improves the communication capacity of the network system, but also makes full use of the bandwidth of the optical fiber, and it has many advantages such as simple expansion and reliable performance, especially it can be directly connected. Entering a variety of businesses makes its application prospects very bright.

In the analog carrier communication system, in order to make full use of the bandwidth resources of the cable and increase the transmission capacity of the system, a frequency division multiplexing method is usually used. That is, signals of several channels are simultaneously transmitted in the same cable, and the receiving end filters the signals of each channel by using a band pass filter according to different carrier frequencies.

Similarly, optical frequency division multiplexing can also be used in optical fiber communication systems to increase the transmission capacity of the system. In fact, such multiplexing methods are very effective in fiber-optic communication systems. Different from the frequency division multiplexing in the analog carrier communication system, in the optical fiber communication system, the light wave is used as the carrier of the signal, and the low loss window of the optical fiber is divided into several according to the frequency (or wavelength) of each channel light wave. Channels to achieve multiplexed transmission of multiple optical signals in a single fiber.

Since some optical devices (such as filters with narrow bandwidths, coherent light sources, etc.) are not yet mature, it is very difficult to realize optical frequency division multiplexing (coherent optical communication technology) with very dense optical channels, but Based on current device levels, frequency division multiplexing of optically separated channels has been achieved. The multiplexing of optical channels with large intervals (even on different windows of optical fibers) is often called optical wavelength division multiplexing (WDM), and DWDM with smaller channel spacing in the same window is called dense wavelength division multiplexing (DWDM). ). With the advancement of technology, modern technology has been able to achieve nano-level multiplexing of wavelength intervals, and even achieve a few nanometer-scale multiplexing with a wavelength interval of zero. It is only stricter in the technical requirements of the device, so 1270nm A band of 20 nm wavelength to 1610 nm is called coarse wavelength division multiplexing (CWDM).

The structure and spectrum of the DWDM system are shown in the figure. The optical transmitter at the transmitting end emits optical signals with different wavelengths and accuracy and stability to meet certain requirements, and is multiplexed together by an optical wavelength multiplexer to feed an erbium-doped fiber power amplifier (the erbium-doped fiber amplifier is mainly used to compensate for the multiplexer). The power loss and the transmission power of the optical signal are increased, and then the amplified multi-path optical signal is sent to the optical fiber transmission, and the optical line amplifier can be determined with or without the optical line amplifier according to the situation, and the optical preamplifier is received at the receiving end (mainly used for Increase the receiving sensitivity to extend the transmission distance. After amplification, the optical wavelength splitter is sent to decompose the original optical signals.


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