CWDM vs. DWDM：What Are the Differences？

It’s known that WDM(Wavelength Division Multiplexing) is divided into DWDM(Dense Wavelength Division Multiplexing) and CWDM(Coarse Wavelength Division Multiplexing). With respect to these two types, there is no doubt that DWDM(Dense Wavelength Division Multiplexing) is the first choice in the fiber applications field. However, due to its high price, manufacturers who are lack of finances are hesitant to purchase it. At this time, most of them prefer to choose CWDM with lower cost. As for difference between DWDM and CWDM, it’s far more than this. Today, this article will make an introduction in a way of CWDM vs. DWDM by Gigalight.

1.    What Is CWDM ？

CWDM is a wavelength multiplexing technology for city and access networks. Transmission is realized using 18 channels with wavelengths between 1270 nm and 1610 nm. Due to the channel spacing of 20 nm cost-effective lasers can be used. The channel width itself is 13 nm. The remaining 7 nm is designed to secure the space to the next channel. Moreover, CWDM is very simple in terms of network design, implementation, and operation. CWDM works with few parameters that need optimization by the user.

CWDM highlights

l  Up to 18 CWDM wavelength over one pair of fiber

l  CWDM channel spacing 20 nm, 1270 nm to 1610 nm

l  Distances up to 120 km

l  Cost-effective WDM solution

l  Scalable by hybrid CWDM/DWDM - perfect solution for your investment

 2.    What Is DWDM ？

DWDM is a technology that puts data from different sources together on an optical fiber, used in fiber optics to increase bandwidth over existing fiber optic backbones, and is with each signal carried at the same time on its own separate light wavelength. The “dense” here means that the wavelength channels are very close to each other.        Besides, DWDM, up to 80 (and theoretically more) separate wavelengths or channels of data can be multiplexed into a lightstream transmitted on a single optical fiber. DWDM systems require complex calculations of balance of power per channel, which is further complicated when channels are added and removed or when it is used in DWDM networks ring, especially when systems incorporate optical amplifiers.

DWDM highlights

l  Up to 96 DWDM wavelength over one pair of fiber

l  DWDM channel spacing 0.8 nm (100 GHz grid) or 0.4 nm (50 GHz grid)

l  Distances over 1,000 km can be achieved with the use of optical amplifier

l  DWDM wavelength: 1528 nm (channel 61) to 1563 nm (channel 17)

Seen from the brief  introductions of CWDM and DWDM, they distinguish in wavelength spacing, transmission distance. Well, actually, they also  differ in cost, optic modulation, power requirements and so on. The following content will be involved in CWDM and DWDM comparison from perspectives of wavelength spacing, transmission distance, cost, optic modulation, power requirements one by one.

CWDM vs. DWDM

3.    CWDM vs. DWDM: Which One Is Better? 

In wavelength spacing, 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. Unlike CWDM, DWDM connections can be amplified and can therefore be used for transmitting data much longer distances.

In transmission distance, DWDM is available for a longer distance transmission by keeping the wavelengths tightly packed. It can transmit more datum over a larger run of cable with less interference than CWDM system. CWDM system cannot transmit data over long distance as the wavelengths are not amplified. Usually, CWDM can transmit data up to 100 miles (160km).

In cost, the DWDM cost is higher than CWDM cost. Due to the uneven distribution of temperature in wide optical wavelength range, and temperature is hard to be tuned, which results in the high cost. While CWDM can make it so that the cost of CWDM is reduced in a large scale, which is now 30% of DWDM cost.

In optic modulation, they are different from each other. The optic modulation of CWDM adopts the electronic tuning instead of non-cooled laser. However, on the contrary, the optic modulation of DWDM adopts the cooled laser and utilizes the temperature for tuning.

In the power requirements, DWDM has significantly higher power requirements than CWDM. For example, DWDM lasers are temperature-stabilized with peltier coolers integrated into their module package. The cooler  with associated monitor and control circuitry consumes around 4W per wavelength. Meanwhile, an uncooled CWDM laser transmitter uses about 0.5W of power.

4.    Conclusion

By the CWDM and DWDM comparison, the difference between CWDM and DWDM is apparent. Although they respectively have their own unique advantages, and it seems that CWDM will be more attractive for carriers who need to upgrade their networks to accommodate current or future traffic needs while minimizing the use of valuable fiber strands, on account that CWDM’s ability to accommodate Ethernet on a single fiber enables converged circuit networks at the edge, and at high demand access sites. Of course, if out of consideration of bandwidth and transmission distance, DWDM is also a good choice. In a word, it’s up to one’s specific demands.