In the construction of metropolitan area networks (especially long-distance OTN optical transmission networks), wavelength division transmission equipment is particularly important. DWDM dense wavelength division multiplexing equipment has long-distance and high bandwidth transmission capabilities; CWDM coarse wavelength division multiplexing equipment has relatively Low cost. So if you choose the right wavelength division multiplexing equipment to build a cost-effective optical transmission system?
The difference between CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment
At present, the effective method to solve the continuous increase of information transmission bandwidth is to use CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment, but they are different in many aspects.
1. The channel spacing between CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment
Channel spacing is defined as the difference in nominal carrier frequency between two adjacent optical channels, and is generally used to prevent inter-channel interference. CWDM wavelength division multiplexing equipment has a wider spacing than DWDM wavelength division multiplexing equipment. It can transmit 18 wavelengths in a spectral grid from 1270 nm to 1610 nm, with a channel spacing of 20 nm. The DWDM wavelength division multiplexing equipment can transmit 40, 80 or even more wavelengths, and the channel spacing can be 0.8 nm (also 1.6 nm and 0.4 nm).
How to choose CWDM-DWDM equipment in optical transmission network
2. The transmission distance between CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment
Because the wavelength of dense wavelength division multiplexing equipment (DWDM) is highly integrated in the optical fiber transmission process, DWDM wavelength division multiplexing equipment can transmit longer distances than CWDM wavelength division multiplexing equipment. CWDM wavelength division multiplexing equipment currently cannot achieve unlimited distance transmission, and its maximum transmission distance is only 160 kilometers, while the transmission distance of DWDM wavelength division multiplexing equipment far exceeds that of CWDM wavelength division multiplexing equipment.
3. Modulated lasers for CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment
The system of CWDM wavelength division multiplexing equipment has low requirements on the technical indicators of the laser, and generally uses uncooled lasers; the system of DWDM wavelength division multiplexing equipment needs to use a cooling laser, and the cooling laser adopts a temperature adjustment method to ensure the DWDM system With better performance, higher safety and longer service life, DWDM wavelength division multiplexers consume more energy than CWDM wavelength division multiplexing equipment that uses uncooled lasers.
4. The cost of CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment
The system of DWDM wavelength division multiplexing equipment has non-uniform temperature distribution in a wide wavelength range, so when the cooling laser technology is used to adjust the temperature, the use cost of the system of DWDM wavelength division multiplexing equipment is increased. In addition, the system of DWDM wavelength division multiplexing equipment is usually four to five times more expensive than the system of CWDM wavelength division multiplexing equipment. However, with the increasing popularity of dense wavelength division multiplexers (DWDM), the price of DWDM optical modules is nearly 30%-35% lower than that of CWDM optical modules.
CWDM/DWDM wavelength division multiplexing equipment usage and transmission comparison
1. The usage of CWDM/DWDM wavelength division multiplexing equipment
As people’s requirements for bandwidth are getting higher and higher, Dense Wavelength Division Multiplexing (DWDM) devices have made great progress in reducing costs, and are therefore more and more favored in the market. However, coarse wavelength division multiplexing equipment (CWDM) still has a higher price advantage in scenarios where the connection rate is lower than 10G and short-distance transmission. In the network construction of low data rate, it is still the most feasible equipment at present.
2. Hybrid transmission of CWDM/DWDM wavelength division multiplexing equipment
CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment each have their own advantages in OTN networks. The advantage of CWDM wavelength division multiplexing equipment is that it can use relatively low-cost distributed feedback lasers that do not require cooling and low prices. The passive filter, therefore the CWDM wavelength division multiplexing equipment system is currently widely used in the DWDM wavelength division multiplexing equipment system. Although CWDM technology can be used in the DWDM system to use cheaper optical modules, the CWDM channel spacing is relatively large, so the number of wavelengths available in the system will be reduced, and this also limits the transmission capacity of the system, so in a certain To a certain extent, it still can’t keep up with the non-hybrid DWDM wavelength division multiplexing equipment.
It can be seen from the above analysis that in the future, CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment will complement each other rather than replace each other.
How to build a CWDM/DWDM wavelength division multiplexing equipment network case analysis
1. User needs
(1) Extension and upgrade: Connect 40ch DWDM wavelength division multiplexing equipment to the 1550nm channel of 8ch CWDM wavelength division multiplexing equipment to achieve channel combination.
(2) Node requirements: The link is 70km long, and two nodes need to be added at 25km and 55km.
2. Scheme design
(1) Due to the limitation of bandwidth, it is impossible to realize the expansion of 40 DWDM channels. Therefore, Amini engineers adopted 8ch C27-C34 DWDM wavelength division multiplexing equipment to meet customer application requirements.
(2) Since the loss of wavelength division multiplexing equipment, OADM and total optical fiber is less than or equal to 24dB, the use of amplifiers can amplify the output of a single channel to 8db, thereby optimizing link signal quality and reducing errors.
(3) Add 1ch OADM to the nodes to download and upload signals.
Summarize
So far, if the user’s WDM network needs more channels, they must all be converted to use DWDM wavelength division multiplexing equipment. Because the wavelength interval of DWDM wavelength division multiplexing equipment is small, it allows a large increase in the number of channels, but the cost of each channel also increases significantly. Therefore, users need to evaluate the future development of their business volume and decide whether to install CWDM wavelength division multiplexing equipment with relatively low flexibility at a lower initial cost, or install flexibility at a higher initial cost. DWDM wavelength division multiplexing equipment.
