In the field of telecommunications, data center connectivity, and video transport, fiber optic cabling is highly desirable. However, the reality is that the fiber optic cabling is no longer an economical or feasible choice to implement for each individual service. Thus using a Wavelength Division Multiplexing (WDM) for expanding the capacity of the fiber on the existing fiber infrastructure is highly advisable. WDM is a technology that multiplexes multiple optical signals onto a single fiber by using different wavelengths of laser light. A quick study of WDM fields will be put on CWDM and DWDM. They are based on the same concept of using multiple wavelengths of light on a single fiber. But they both have their merits and demerits.
What is CWDM?
CWDM supports up to 18 wavelength channels transmitted through a fiber at the same time. To achieve this, the different wavelengths of each channel are 20nm apart. DWDM, supports up to 80 simultaneous wavelength channels, with each of the channels only 0.8nm apart. CWDM technology offers a convenient and cost-efficient solution for shorter distances of up to 70 kilometers. For distances between 40 and 70 kilometers, CWDM tends to be limited to supporting eight channels.
A CWDM system commonly supports eight wavelengths per fiber and is designed for short-range communications, using wide-range frequencies with wavelengths spread far apart.
Since CWDM is based on 20-nm channel spacing from 1470 to 1610 nm, it's typically deployed on fiber spans up to 80km or less because optical amplifiers cannot be used with large spacing channels. This wide spacing of channels allows the use of moderately priced optics. However, the capacity of the links as well as the distance supported are less with CWDM than with DWDM.
Generally, CWDM is used for lower cost, lower capacity (sub-10G) and shorter distance applications where cost is an important factor.
More recently, the prices for both CWDM and DWDM components have become reasonably comparable. CWDM wavelengths are currently capable of transporting up to 10 Gigabit Ethernet and 16G Fiber Channel, and it is quite unlikely for this capacity to further increase in the future.
What is DWDM?
Unlike CWDM, DWDM connections can be amplified and can, therefore, be used for transmitting data much longer distances.
In DWDM systems, the number of multiplexed channels is much denser than CWDM because DWDM uses tighter wavelength spacing to fit more channels onto a single fiber.
Instead of the 20 nm channel spacing used in CWDM (equivalent to approximately 15 million GHz), DWDM systems utilize a variety of specified channels spacing from 12.5 GHz to 200 GHz in the C-Band and sometimes the L-band.
Today's DWDM systems typically support 96 channels spaced at 0.8 nm apart within the 1550 nm C-Band spectrum. Because of this, DWDM systems can transmit a huge quantity of data through a single fiber link as they allow for many more wavelengths to be packed onto the same fiber.
DWDM is optimal for long-reach communications up to 120 km and beyond due to its ability to leverage optical amplifiers, which can cost-effectively amplify the entire 1550 nm or C-band spectrum commonly used in DWDM applications. This overcomes long spans of attenuation or distance and when boosted by Erbium Doped-Fiber Amplifiers (EDFAs), DWDM systems have the capability to carry high amounts of data across long distances spanning up to hundreds or thousands of kilometers.
In addition to the capability of supporting a greater number of wavelengths than CWDM, DWDM platforms are also capable of handling higher speed protocols as most optical transport equipment vendors today commonly support 100G or 200G per wavelength while emerging technologies are allowing for 400G and beyond.
DWDM vs CWDM wavelength spectrum:
CWDM has a wider channel spacing than DWDM -- the nominal difference in frequency or wavelength between two adjacent optical channels.
CWDM systems typically transport eight wavelengths with a channel spacing of 20 nm in the spectrum grid from 1470 nm to 1610 nm.
DWDM systems, on the other hand, can carry 40, 80, 96 or up to 160 wavelengths by utilizing a much narrower spacing 0.8/0.4 nm (100 GHz/50 GHz grid). DWDM wavelengths are typically from 1525 nm to 1565 nm (C-band), with some systems also capable of utilizing wavelengths from 1570 nm to 1610 nm (L-band).
CWDM Advantages:
1. Low Cost
CWDM is much cheaper than DWDM because of hardware costs. CWDM system uses cooled lasers that is much cheaper than DWDM uncooled lasers. In addition, The price of DWDM transceivers is typically four or five times more expensive than that of their CWDM modules. Even the operating costs of the DWDM is higher than CWDM. So CWDM is an ideal choice for those who have a limitation in funding.
2. Power Requirement
Compared with CWDM, the power requirements for DWDM are significantly higher. As DWDM lasers together with associated monitor and control circuitry consume around 4 W per wavelength. Meanwhile, an uncooled CWDM laser transmitter uses about 0.5 W of power. CWDM is a passive technology that uses no electrical power. It has positive financial implications for internet operators.
3. Easy Operation
CWDM systems use simpler technology with respect to DWDM. It uses LED or Laser for power. The wave filters of CWDM systems are smaller and cheaper. So they are easy to be installed and used.
DWDM Advantages:
1. Flexible Upgrade
DWDM is flexible and robust with respect to fiber types. DWDM upgrade to 16 channels is viable on both G.652 and G.652.C fibers. Originally from the fact that DWDM always employs the low loss region of the fiber. While 16 channel CWDM systems involve transmission in the 1300-1400nm region, where attenuation is remarkably higher.
2. Scalability
DWDM solutions allow the upgrade in steps of eight channels to a maximum of 40 channels. They allow a much higher total capacity on the fiber than a CWDM solution.
3. Long Transmission Distance
DWDM employs the 1550 wavelength band which can be amplified using conventional optical amplifiers (EDFA’s). It enhances transmission distance to hundreds of kilometers.
The following picture will give you a visual impression of the differences between CWDM and DWDM.
Post time: Jun-14-2022