What is the definition of DWDM?
867 2022-01-04

What is the definition of DWDM?


DWDM is a combination of a set of optical wavelengths that can be transmitted by one fiber. This is a laser technology used to increase bandwidth on existing fiber backbones. More specifically, the technique is to multiplex the tight spectral spacing of individual fiber carriers in a given fiber to take advantage of the achievable transmission performance (e.g., to achieve minimal dispersion or attenuation). Thus, with a given information transmission capacity, the total number of fibers required can be reduced.

DWDM is able to combine and transmit 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 collected in March 2013, due to the adoption of DWDM technology, a single fiber can transmit more than 150 different wavelengths of light waves simultaneously, and the maximum speed of each beam can reach 10Gb/s. As vendors add more channels to each fiber, terabits per second transfer speed 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.

Background

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 pure optical devices for long-wave scheduling breaks the limit of processing speed of electronic devices. On the basis of SDH technology, the optical fiber propagation capacity can be greatly improved. The current commercial application rate of 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. [1]

 

The first proposed party for DWDM technology is Lucent, whose Chinese translation is dense optical multiplexing. DWDM technology was introduced in 1991. Specifically, it is a combination of a group of optical wavelengths transmitted by an optical fiber, which is a laser technology used to increase the bandwidth on existing fiber backbone networks. 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.

 

Principle

 

In the actual operation, in order to make reasonable use of the broadband resources generated by the single-mode fiber in the low-loss region of 1.55 pm, it is necessary to divide the low-loss region of the fiber into multiple optical channels according to different frequencies and wavelengths, and need to be in each The optical channel establishes the carrier wave, which is what we call the optical wave. At the same time, the splitter combines the signals of different specified wavelengths at the transmitting end, and the combined signals are collectively transmitted into one optical fiber for signal transmission. When transmitting to the receiving end, these are combined with different wavelengths using an optical demultiplexer. The decomposition of the signals of different light waves into the initial state realizes the function of transmitting a plurality of different signals in one optical fiber.

 

System structure

 

DWDM is structurally divided and currently has an integrated system and an open system. Integrated system: The optical signal of the terminal of the single optical transmission equipment required to be accessed is G. 692 standard light source. The open system is at the front end of the combiner and the back end of the splitter, plus the wavelength conversion unit OTU, which will be commonly used. The 957 interface wavelength is converted to G. 692 standard wavelength optical interface. So, open systems use wavelength conversion technology? Make any satisfaction G. The light signal required by the 957 recommendation can be converted to G. by wavelength conversion after using the photo-electric-optical method. The standard wavelength optical signal required by 692 is then transmitted by wavelength division multiplexing on the DWDM system.

 

The current DWDM system can provide 16/20 wave or 32/40 wave single fiber transmission capacity, up to 160 waves, and flexible expansion capability. Users can build a 16/20 wave system at the beginning, and then upgrade to 32/40 waves as needed, which can save initial investment. The principle of its upgrade scheme: one is to upgrade the 16-band and 16-wave of the C-band red band to the 32-wave scheme; the other is to use the Interleaver, and the C-band is upgraded from the 200 GHz interval 16/32 wave to the 100 GHz interval 20/. 40 waves. For further expansion, the C+L band expansion scheme can be provided to further expand the system transmission capacity to 160 waves.

 

DWDMs that are currently used by major domestic operators are mostly open DWDM systems. In fact, integrated Dense Wavelength Division Multiplexing systems have their own advantages:

 

1. The combiner and splitter of the integrated DWDM system are used separately at the originating end and the receiving end, that is, only the combiner at the origin, only the splitter at the receiving end, and both the receiving end and the transmitting end are removed. OTU conversion equipment (this part is more expensive)? Therefore, the investment in DWDM system equipment can be saved by more than 60%.

 

2. The integrated DWDM system uses only passive components (such as: combiner or splitter) at the receiving end and the transmitting end. The telecom operation unit can directly order the device manufacturer, reduce the supply link, and lower the cost, thereby saving equipment costs. .

 

3. The open DWDM network management system is responsible for: OTM (mainly OTU), OADM, OXC, EDFA monitoring, and its equipment investment accounts for about 20% of the total investment of the DWDM system; while the integrated DWDM system does not require OTM equipment, The network management is only responsible for the monitoring of OADM, OXC, and EDFA. It can introduce more manufacturers to compete, and its network management cost can be saved by about half compared with the open DWDM network management.

 

4. Since the multiplexed wave/demultiplexing device of the integrated DWDM system is a passive device, it is convenient to provide multiple services and multi-rate interfaces, as long as the wavelength of the optical transceiver of the service end device meets the requirements of G. The 692 standard can be used for any services such as PDH, SDH, POS (IP), ATM, etc., supporting PDH and SDH at various rates such as 8M, 10M, 34M, 100M, 155M, 622M, 1G, 2.5G, and 10G, ATM and IP Ethernet? Avoiding the open DWDM system due to OTU, can only use SDH, ATM or IP Ethernet devices with optical wavelength (1310nm, 1550nm) and transmission rate determined by the purchased DWDM system? It is impossible to use other interfaces at all.

 

5. If the laser device module of optical transmission equipment such as SDH and IP router is uniformly designed as the standard geometric size pin, the interface is standardized, which is convenient for maintenance and plugging, and the connection is reliable. In this way, the maintenance personnel can freely replace the laser head of a specific color wavelength according to the wavelength requirement of the integrated DWDM system, which provides a convenient condition for the fault maintenance of the laser head and avoids the drawback that the whole board must be replaced by the whole factory before. High maintenance costs.

 

6. The color wavelength light source is only slightly more expensive than the ordinary 1310nm and 1550nm wavelength light sources. For example, the 2.5G color wavelength light source is currently more than 3,000 yuan, but when it is connected to the integrated DWDM system, it can The cost of the cost system is reduced by nearly 10 times, and with the large number of applications of color wavelength sources, the price will be close to that of ordinary light sources.

 

7. The integrated DWDM device is simple in structure and smaller in size, and only about one-fifth of the space occupied by the open DWDM saves the resources of the computer room.

In summary, the integrated DWDM system should be widely used in a large number of DWDM transmission systems, and gradually replace the dominant position of the open DWDM system. Considering that optical transmission equipment with a large number of common light sources is currently in use on the network, it is recommended to use integrated and open-compatible hybrid DWDM to protect the upfront investment.

 

System principle

 

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

 

Compared with the universal 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 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 usually 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 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.

 

OADM and OXC functions of DWDM system

OADM can provide optical signals of wavelengths at any optical relay site as needed (currently 8 waves can be achieved). This function works with OXC to send any optical signal from any port to any wavelength of the system. So that even if the optical signals of the two upper ports are the same, they will not cause blocking. The same way, the port assignment function can also be used to transfer a certain downstream wavelength to any port as needed, which greatly expands the flexibility of the OADM application. In addition, the combination of OADM and OXC can provide protection modes such as two-fiber unidirectional multiplex section protection, two-fiber bidirectional multiplex section protection, and channel protection, so that the self-healing ring network can be realized, and the system performance is safe. reliable.

 

Application of DWDM technology in power system

The advent of new communication devices does not indicate a denial of the original equipment and technology, but should be inheritance, development and innovation. The 64k Subrate—PDH—SDH—DWDM reflects and follows this principle. From the current analysis of the application status of power systems, the DWDM technology level of wavelength division multiplexing cannot completely replace SDH, but it can cooperate with SDH technology division, complement each other, optimize the power communication network, comprehensively improve communication bandwidth, and ensure the security of network systems. And stable.

 

From the current dense optical wave multiplexing (DWDM) equipment and technology, the device not only needs to use components such as optical amplifier, splitter, multiplexer, dispersion compensation, but also more fiber jumpers. In theory, DWDM ratio SDH devices have a higher probability of failure, so it is unscientific to use DWDM to transmit scheduling data.

 

From another perspective, DWDM, as a complement and complement to SDH, is fully capable of providing a protection channel for scheduling data transmission. In addition, the network management data of SDH is based on packet transmission, and most of them are Ethernet. Therefore, WDM DWDM technology can provide protection channel for SDH network management, and SDH can also stabilize DWDM network management to provide protection channel.

 

We can predict that the promotion and implementation of dense light wave multiplexing (DWDM) technology will provide strong support in high-definition conference TV, remote video surveillance and NGN to enhance the power communication bandwidth. The biggest advantage is high performance and low price. Scientifically and rationally dividing DWDM and SDH services can give full play to their respective advantages, reduce the pressure on network management, and improve the communication operation management level.