In the applications related to optical transport network (OTN), coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM) is considered as the primary technologies of wavelength division multiplexing (WDM). When it comes to enhancing the bandwidth and space utilization of an existing or new fiber optics network, one of these technologies is utilized. Although the purpose of using both of these technologies is the same, these technologies differ in several aspects. Therefore, to make an application-suited choice, one must know the differences between these technologies. This post discusses differentiating factors and their impact on the applications.

 

What is Wavelength Division Multiplexing (WDM)?

Wavelength division multiplexing (WDM) is a signal multiplexing technology which multiplexes the number of transmission channels in a fiber optic cable utilizing various wavelengths of laser light. It enables multi-signal transmission via a single fiber optic cable by uniformly distributing the wavelength in order to avoid frequency interactions. This technology enables bi-directional communication and signals multiplication capacity.

There are two types of wavelength division multiplexing (WDM), namely, coarse wavelength division multiplexing (CWDM) and dense wavelength division (DWDM). Let us discuss both of these technologies individually.

Gain an Overview of Coarse Wavelength Division Multiplexing (CWDM)

The term coarse wavelength division multiplexing (CWDM) initially described a number of channel configurations via a single fiber optic cable. It was quite a general description of the term, as the use of erbium-doped fiber amplifiers (EDFAs) for wavelength distribution across a number of channels and frequencies was rampant. However, according to ITU-T G.694.2 standards established in the year 2002, CWDM features wavelengths ranging from 1270nm to 1610 nm whereas the channel spacing in CWDM is 20 nm apart.

CWDM is designed for short-range communication with the transmission of up to eight wavelengths via a single fiber. Since it uses a wide range of frequencies, the channels are spaced apart. It can commonly be used for 80km or even shorter distance since the optical amplifiers cannot be used due to wide channel spacing.

What is Dense Wavelength Division Multiplexing (DWDM)?

Dense wavelength division multiplexing (DWDM) is another version of wavelength division multiplexing (WDM) which enables multiple wavelength transmission at close spacing. This means in DWDM the multiplexed channels are spaced quite close to each other creating a dense transmission environment inside the fiber optic cable. DWDM multiplexes the wavelengths ranging from 1525 nm to 1565 nm (C-Band) or 1570 nm to1610 nm (L-Band). It is specifically designed for long-distance transmission up to 120 km. It also supports the use of optical amplifiers as the channel spacing is quite nearby. This technology is also suitable for high-speed protocols, thus, it can transmit 100 to 400 G per wavelength.

Both these technologies, CWDM, and DWDM serve the same purpose of enabling multi-channel transmission via a single fiber optics cable without mixing the frequencies. Therefore, CWDM vs DWDM is always an ongoing comparison in the market. When it comes to selecting signal multiplexing technologies, these two technologies are often compared.

The next section focuses on some differentiating factors of CWDM vs DWDM.

Differentiating Aspects of CWDM vs DWDM

The following are some factors based on which the comparison between CWDM vs. DWDM is made.

  • Wavelength Spectrum: The CWDM system transmits up to 8 wavelengths under the wavelength spectrum from 1470 nm to 1610 nm. The common wavelengths in CWDM are 1470 nm, 1490 nm, 1510 nm, 1530nm, 1550 nm, 1570 nm, 1590 nm, and 1610 nm. This uniformly distributed range of wavelengths is transmitted via a single fiber optics cable in CWDM.

On the other hand, the DWDM system transmits a large number of wavelengths. The number of wavelengths transmitted via a fiber optic cable by using DWDM can range from 40 to 160. Therefore, the wavelength spectrum of DWDM is comparatively broader than CWDM.

  • Channel Spacing: As mentioned earlier, CWDM features 20 nm of channel spacing, whereas, DWDM features narrow spacing of 0.4 nm or 0.8 nm.
  • Transmission Distance: The CWDM system is only suitable for a limited transmission distance of around 80 km. In rare cases, this transmission distance can be extended to 160 km. On the other hand, the DWDM system can be used for unlimited transmission distance as it supports the use of optical amplifiers.
  • Modulation Laser: CWDM uses uncooled lasers which restricts the adoption of high-speed protocols of transmission via fiber optics. However, DWDM on the other hand use cooled lasers that enable high-speed transmission protocols. Therefore, the overall transmission rate is higher in DWDM due to laser modulation. The cooling laser in the DWDM system adopts the fiber temperature during transmission assuring the safe operation of a fiber optics cable.
  • Cost: Cost is an important comparison factor here. The cost of a DWDM system is about 5 times higher than CWDM systems. The cost of cooling lasers increases the cost of the DWDM system.

Considering these mentioned factors can help you choose between CWDM and DWDM. However, in order to use these technologies in real-time applications, you will need to consider their power-source conditions too.

Active vs Passive CWDM/DWDM

The CWDM and DWDM both are available in two types of power source conditions, namely, active and passive. According to the application, you can choose types of CWDM or DWDM systems.

The passive CWDM/ DWDM systems are the non-powered type of optical transmission systems. In such types of systems, the transceivers are directly integrated inside the device. No external power source is necessary for these types of optical transmission systems. Common examples of these systems are IP switches, CWDM SFP modules, etc.

On the other hand, the active CWDM/DWDM devices are powered by the external stand-alone AC or DC power sources. The primary benefit of active CWDM/DWSM systems is that these modules extend the range of short-range output signals while channeling between CDWM or DWDM transmission modules.

Considering the requirements of your application, you can select the type of CWDM or DWDM systems. Commonly, to implement CWDM or DWDM system to your fiber optics transmission, DWDM/CWDM SFP pluggable modules, DWDM/CWDM Mux/Demux optical modules are chosen. However, you must ensure to buy these products from prominent manufacturers to get optimum efficiency.