CWDM or DWDM Wavelength Division Multiplexing Equipment

Wavelength division multiplexing equipment is particularly important in metropolitan area network construction especially long-distance OTN optical transmission network，. DWDM dense wavelength division multiplexing equipment has long-distance, high-bandwidth transmission capabilities; While lower cost can choose CWDM coarse wavelength division multiplexing equipment . How to choose the right wavelength division multiplexing equipment to build a cost-effective optical transmission system?

What is the difference between CWDM wavelength division multiplexing equipment and DWDM wavelength division multiplexing equipment?
At present, the effective way to increase 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.Channel spacing Difference
The channel spacing is defined as the difference between the nominal carrier frequencies between two adjacent optical channels and is generally used to prevent inter-channel interference. CWDM has a wider spacing than DWDM wavelength division multiplexing equipment. It can transmit 18 wavelengths in the spectral grid from 1271 nm to 1611 nm with a channel spacing of 20 nm. DWDM wavelength division multiplexing equipment can transmit 40, 80 or 160 wavelengths, and the channel spacing can be 0.8 nm.
2. Transmission distance
DWDM wavelengths are highly integrated during fiber transmission, so it can transmit longer distances than CWDM. CWDM is currently unable to achieve unlimited distance transmission with max transmission distance 160km, while the transmission distance of DWDM far exceeds that of CWDM.
3. Modulated lasers different
The system of CWDM has lower requirements on the technical specifications of the laser, and generally a non-refrigerated laser can be adopted; the system of DWDM needs to use a cooling laser which adopts a temperature adjustment method to ensure the DWDM system with better performance, higher safety and longer service life, so DWDM consumes more energy than CWDM
4. Cost
The system of DWDM has uneven temperature distribution in a wide wavelength range, so the cooling laser technology is used to adjust the temperature, hence the use cost of the system of DWDM 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. However, with the increasing popularity of Dense Wavelength Division Multiplexer (DWDM), the price of DWDM optical module is nearly 20%-25% lower than that of CWDM optical module
Which is Better?
Usage of CWDM/DWDM wavelength division multiplexing equipment
As increasing higher requirements for bandwidth, DWDM has made great progress in cost reduction to make it more popular in market, However, coarse wavelength division multiplexing equipment (CWDM) still has a higher price advantage in the connection rate of less than 10G and short-distance transmission scenarios which keeps it as most feasible device In the construction of low data rate networks at present
Hybrid transmission of CWDM/DWDM
CWDM and DWDM have their own advantages in the OTN network. Due to CWDM use a distributed feedback laser with low cost and no cooling, and low price, it is currently widely used in the system of DWDM wavelength division multiplexing equipment. However the relatively large CWDM channel spacing reduces the number of available wavelengths of the system which limits the transmission capacity of the system, to some extent, it still can’t keep up with the non-hybrid DWDM wavelength division multiplexing equipment

Above analysis indicates CWDM wavelength division multiplexing equipment and DWDM will complement each other rather than replace each other.
How to build CWDM/DWDM wavelength division multiplexing equipment network case analysis
1. User requirements
(1) Expansion and upgrade: Connect the 40ch DWDM wavelength division multiplexing device to the 1550nm channel of the 8ch CWDM wavelength division multiplexing device to achieve channel combination.
(2) Node requirements: The link is 65km long, and two nodes need to be added at 15km and 50km.
2. Scheme design
(1) Due to the limitation of bandwidth, the expansion of 40 DWDM channels cannot be achieved, so the engineers adopted 8ch C27-C34 DWDM wavelength division multiplexing equipment to meet the customer’s application needs.
2) Because the loss of WDM equipment, OADM and total fiber is ≤23dB, the amplifier can amplify a single channel output to 8db, thereby optimizing the quality of the link signal and reducing errors.
(3) Add 1ch OADM to the nodes to download and upload signals.
Conclusion
DWDM wavelength division multiplexing equipment must be adopted when the user network requires more channels, it allows a large increase in the number of channels with significantly cost increases. Therefore, the future development of user business volume should be evaluated to decide whether to install initially relatively low cost CWDM without flexibility or higher initial cost DWDM wavelength division multiplexing equipment with flexibility