What's the Difference Between CWDM and DWDM?

DWDM dense wavelength division multiplexing (WDM) equipment is especially important in metro network construction (especially long-distance OTN optical transmission network), DWDM dense wavelength division multiplexing (DWDM) equipment has long-distance and high bandwidth transmission capability; CWDM coarse wavelength division multiplexing (CWDM) equipment has lower cost.

What is the Difference Between CWDM Equipment and DWDM Eequipment?

The current effective way to solve the increasing bandwidth of information transmission is to use CWDM equipment and DWDM equipment, but they are different in many aspects.

Channel Spacing Between CWDM Equipment and DWDM Equipment

The 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. 160 wavelengths with a channel spacing of 0.8 nm.

CWDM Equipment and DWDM Equipment Transmission Distance

Because the wavelengths of dense wavelength division multiplexing (DWDM) devices are highly integrated in the fiber optic transmission process, DWDM WDM devices are able to transmit longer distances than CWDM WDM devices. WDM equipment.

CWDM Equipment and DWDM Equipment Modulation Laser

The system of CWDM equipment has lower requirements on the technical index of the laser, generally using uncooled lasers; the system of DWDM equipment needs to use cooling lasers, cooling lasers use temperature regulation to ensure that the DWDM system has better performance, higher safety and longer service life, so DWDM WDM is better than using uncooled lasers. Therefore, DWDM WDM devices consume more energy than CWDM WDM devices with uncooled lasers.

Cost of CWDM Equipment and DWDM Equipment

The system of DWDM equipment increases the cost of using the system of DWDM equipment because the temperature distribution is not uniform over a wide range of wavelengths, so when the cooling laser technology is used to regulate the temperature, it increases the cost of using the system of DWDM equipment. In addition, DWDM systems are typically four to five times more expensive than CWDM systems. However, with the increasing popularity of dense wavelength division multiplexers (DWDM), the price of DWDM optical modules is nearly 20-25% lower than the price of CWDM optical modules.

Which is better to use for CWDM/DWDM equipment?

Usage of CWDM/DWDM Equipment

Dense Wavelength Division Multiplexing (DWDM) equipment has made great progress in cost reduction due to the increasing demand for bandwidth, and is therefore gaining more and more popularity in the market. However, coarse wavelength division multiplexing (CWDM) equipment still has a high price advantage in connection rates below 10G and in short-range transmission scenarios. It is still the most viable device for network construction at low data rates today.

Hybrid Transmission of CWDM/DWDM Devices

CWDM WDM and DWDM WDM devices each have their own advantages in OTN networks. Since CWDM WDM devices have the advantage of using lower-cost distributed feedback lasers without cooling and inexpensive passive filters, CWDM systems are now widely used in DWDM systems. Although the use of CWDM technology in DWDM systems can also use cheaper optical modules, but because the CWDM channel spacing is relatively large, so the number of wavelengths available to the system will be reduced, and this also limits the transmission capacity of the system, so in a way is still not able to catch up with non-hybrid DWDM wavelength division multiplexing equipment. In the future, CWDM WDM and DWDM WDM devices will complement each other rather than replace each other.

How to Set Up CWDM/DWDM Equipment Network Case Study?

User requirements

1. Expansion and upgrade: connect 40ch DWDM equipment to 1550nm channel of 8ch CWDM equipment to realize channel combination.
   
2. Node requirements: the link length is 65km, two nodes need to be added at 15km and 50km.
   

Program design

1. Due to the limitation of bandwidth, the expansion of 40 DWDM channels cannot be realized, so the engineers of NADDOD use 8ch C27-C34 DWDM equipment to meet the customer’s application requirements.
   
2. Since the loss of WDM equipment, OADM and total fiber is ≤23dB, the output of a single channel can be amplified up to 8db using an amplifier, thus optimizing the link signal quality and reducing errors.
   
3. Add 1ch OADM to the node to download and upload signals respectively.
   

Summary

So far, if the user’s WDM network needs more channels, it must be converted to use DWDM equipment. Because of the small wavelength spacing of DWDM equipment, it allows a large increase in the number of channels, but the cost per channel also increases significantly. Therefore, users need to evaluate the future growth of their service volume and decide whether to install less flexible CWDM equipment at a lower initial cost or more flexible DWDM equipment at a higher initial cost.