Shulou(Shulou.com)11/24 Report--

With the rapid development of communications and the Internet, a variety of high-traffic services such as online on-demand, video chat and video conferencing are emerging. Do you know how these services can reach your mobile phone, computer or TV? The transmission network is like the logistics system in the communication network, which sends all kinds of data, videos and other "packages" to you in real time and efficiently. In the transmission network technology, WDM technology is a logistics master, famous for its advantages of high capacity and saving optical fiber resources. Today, the editor will talk to you about WDM. For the history of the development of transmission technology, you can refer to the History of Optical Transmission. )

What is WDM? If the optical fiber is compared to the highway, different services are equivalent to vehicles entering the highway. If everyone wants to enter the optical fiber transmission in different lanes, they need to queue up to enter, which affects the transmission efficiency. With WDM, different services can be transmitted on the same optical fiber at the same time through WDM technology, which is equivalent to dividing lanes for different vehicles on the highway, allowing different vehicles to run in different lanes at the same time, and improving the transmission efficiency.

To sum up, WDM (Wavelength Division Multiplexing, wavelength Division Multiplexing) is a technology that combines two or more optical signals of different wavelengths at the transmitting end into one optical signal for transmission in the same optical fiber, and then restores the combined optical signals to optical signals of different wavelengths by demultiplexing at the receiver.

As shown in the following figure, at the sending end, WDM converts all kinds of traffic signals entering its system into optical signals of different colors, that is, optical signals of different wavelengths, and synthesizes a color optical signal to be transmitted on the same optical fiber. At the receiving end, the WDM system performs the opposite operation, reducing the color light signal to different color light signal.

What does the WDM system consist of? As long as the lane is divided, can WDM allow different services to be transmitted on the same optical fiber at the same time? It's not that simple. Let's take a look at how WDM does it.

In technical terms, WDM systems are generally composed of OTU (Optical Transponder Unit, optical forwarding unit), combinator / splitter unit, monitoring channel and optical amplifier unit.

So, how do the various parts of WDM work together to complete business transmission? Let's take a look at the transmission process of business in WDM.

1. If the service is to be transmitted in the WDM, the service should be sent to the WDM proprietary truck (that is, the OTU unit), and these service signals should be converted into the standard wavelength optical signals recognized by WDM.

two。 The standard wavelength light signal truck carrying the service is driven to the checkpoint (that is, the combined wave unit), and is arranged to enter different lanes through the checkpoint, and one car is driving on the highway at the same time.

3. The driving condition of the truck needs to be supervised by the patrol car, that is, the monitoring channel to ensure that the service transmission is normal.

4. If the transportation distance is long, we also need to let the truck drive into the unified gas station, that is, through the optical amplification unit, the business signal is regenerated and amplified to ensure that there is no damage to the long-distance transportation of the business.

5. When the service is transported to the terminal, the truck comes out from the inspection station (that is, the split-wave unit) and diverts to the corresponding receiving customer terminal exit, and the service is unloaded from the truck, that is, it is converted into the customer service signal (that is, the service signal without wavelength information) through the OTU unit, and sent to the customer.

What are the categories and applications of WDM? According to the size of lane spacing (that is, according to the wavelength spacing of adjacent optical signals), WDM can be divided into two categories:

CWDM:Coarse Wavelength Division Multiplexing, sparse wavelength division multiplexing. The lane spacing of CWDM is relatively large, usually 20 nm, and there are fewer lanes, with 18 lanes. The optical signal has a wide wavelength range, ranging from 1270 nm to 1610 nm. CWDM technology is generally used in metropolitan area network transmission, especially in communication applications with short distance, high broadband and dense access points, such as network communication within or between buildings.

DWDM:Dense Wavelength Division Multiplexing, dense wavelength division multiplexing. The lane spacing of DWDM is relatively small, which can be 1.6 nm, 0.8 nm, 0.4 nm, 0.2 nm, and the maximum is 192 lanes. DWDM uses C-band, extended C-band and L-band wavelength signals. The C-band and the extended C-band wavelength range is 1525nm~1572 nm. The wavelength range of L-band is 1570 nm~1610 nm. DWDM is suitable for long-distance, large-capacity long-distance trunk network or super-large capacity metro core nodes, such as city-to-city transmission network.

What are the advantages and disadvantages of WDM system? The WDM system has the following four advantages:

The transmission capacity of the WDM system is large, and the single channel of the WDM system can realize the service transmission of more than 100 Gbit / s, and can support 80 waves and above channels, that is, the transmission capacity of the WDM system can exceed 80x100 Gbit / s.

The transmission distance is long, and the transmission distance of the WDM system can exceed 1000 km, which can be transmitted across the seafloor from the northern hemisphere to the southern hemisphere.

The transmission cost is low, and valuable optical fiber resources can be saved. For example, there are 80 2.5 Gbit / s optical services that need to be transmitted. If it is a non-WDM system, each service needs one fiber for sending and receiving, and a total of 160fibers are needed, while the 80x2.5 Gbit / s WDM system only needs two fibers.

It has strong flexibility. WDM system is "transparent" to all kinds of business signals, and can transmit different types of signals, such as digital signals, analog signals, etc., and can synthesize and decompose them. WDM is also an ideal means of capacity expansion. When the network capacity is expanded, it does not need to lay more optical fibers, nor does it need to use high-speed network components, it only needs to increase the number of multiplexed optical paths and equipment, which can increase the transmission capacity of the system to achieve capacity expansion. and the expansion will not have an adverse effect on other multiplexed optical paths.

In addition to the above advantages, WDM has some disadvantages, the most obvious disadvantage is that if a service specifies the channel transmission in the WDM system, the channel can no longer be used by other services, which will result in a waste of resources. For example, on the highway, each type of truck takes a fixed lane, and if the lane is free, other types of trucks are not allowed to use this lane.

In a word, with the rapid expansion of information data, WDM technology acts as a logistics master, constantly transmitting these information data "goods" with higher speed and more reliable performance.

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc)

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