When dealing with OTN (Optical Transport Network), there are two main types of Wavelength Division Multiplexing (WDM) systems: Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM). As two modern WDM technologies, they are both used for increasing the bandwidth of fiber by combining optical signals of different wavelengths on one strand of fiber. But CWDM vs DWDM, what are their differences?
To better understand the difference between CWDM and DWDM, we’d better get to know what’s WDM, CWDM and DWDM in the first place.
WDM is a technology for transporting large amounts of data between sites. It increases bandwidth by allowing different data streams to be sent simultaneously over a single optical fiber network. In this way, WDM maximizes the utilization of fiber and helps to optimize network investments.
As mentioned above, CWDM and DWDM are two technologies developed based on WDM, but with different wavelength patterns and applications. CWDM is a flexible technology that can be deployed on most types of fiber networks. It is typically deployed in point-to-point topology in enterprise networks and telecom access networks. While DWDM is viewed as an option for the metropolitan network. Now it is also used for interconnecting data centers and for financial services networks, and is often deployed in ring topology.
CWDM and DWDM are both effective methods to solve the increasing bandwidth capacity of information transmission at present. But they differ to each other in many aspects. Below parts will introduce some differences between CWDM and DWDM systems.
The channel spacing is defined to be the nominal difference in frequency or wavelength between two adjacent optical channels. CWDM has a wider spacing than DWDM. It is able to transport up to 18 CWDM wavelengths with a channel spacing of 20nm in the spectrum grid from 1271nm to 1611nm. DWDM can carry 40, 80 or up to 160 wavelengths with a narrower spacing of 0.8/0.4nm (100 GHz/50 GHz grid). Its wavelengths are from 1525nm to 1565nm (C band) and 1570nm to 1610nm (L band).
Since DWDM wavelengths are highly integrated in the fiber during light transmission, DWDM is able to reach a longer distance than CWDM. Unlike CWDM system, CWDM is unable to travel unlimited distance. The maximum reach of CWDM is about 160 km. While an amplified DWDM system can go much further.
CWDM system uses the uncooled laser while DWDM system uses the cooling laser. Cooling laser adopts temperature tuning which ensures better performance, higher safety and longer life span of DWDM system. But it is also consumes more power than the electronic tuning uncooled laser used by CWDM system.
Because the range of temperature distribution is nonuniform in a very wide wavelength, so the temperature tuning is very difficult to realize, thus using the cooling laser technique increases the cost of DWDM system. Further more, the DWDM devices are typically four or five times more expensive than that of a CWDM system. However, s DWDM becoming increasingly popular, price of DWDM transceiver is about 20-25% less than a CWDM transceiver. For example, the price of CWDM SFP+ transceiver from FS.COM is about $ 499, while the DWDM SFP+ is sold only at $ 369.
As mentioned above, the primary difference between DWDM and CWDM is the channel spacing (CWDM has almost 100 times wider channel spacing). This makes CWDM is a simpler technology, resulting in advantages and disadvantages of the different systems with regard to cost, performance and so on.
|CWDM Advantages||CWDM Disadvantages|
Lower power consumption
Smaller space requirements
Can use SMF fiber or MMF cable
Can use LED’s or Laser’s for power
Larger individual payloads per channel
Smaller and cheaper wave filters
Cost savings on start up and expansion
Less capacity than DWDM
Regeneration vs amplification
O, A and M functions are not carrier class
|DWDM Advantages||DWDM Disadvantages|
Maximum capacity system available
Maximum distance capability with EDFA’s
Repeater “amp” sites can be reduced
Pay as you grow expansion
Mature O, A and M systems are developed
Need more space
Need more power
Need high accuracy lasers and wave filters
Expensive EDFA’s for amplifiers
Start up costs are more than equivalent CWDM system
Since there is tremendous demand for more and more bandwidth, DWDM is much more favored in the market. And it has experienced great advancement in cost reduction. However, CWDM still has price advantage for connection rates below 10G and for short distances. With low data rates, it is currently most feasible technology. In this way, CWDM and DWDM each provides a unique “fit” in OTN network, and will complement rather than replace each other in the future.
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