CWDM Vs DWDM – A Comprehensive Analysis

Dense Wavelength Division Multiplexing (or DWDM) and Coarse Wavelength Division Multiplexing (CWDM) are the two main types of Wavelength Division Multiplexing that come into context when we deal with Optical Transport Network (OTN). These WDM technologies can increase fiber bandwidth by combining (multiplexing) optical signals traveling at different wavelengths on a single fiber strand. Though the basic working phenomenon behind Coarse and Dense wavelength multiplexing is the same, they have some differences. In this post, we will talk about CWDM vs DWDM.

WDM, DWDM, CWDM Basics

Before we compare CWDM vs DWDM, it is better to know the basic introduction of WDM, CWDM, and DWDM.

What is WDM?

WDM, or Wavelength Division Multiplexing, is a technology available for data transmission between sites. We can achieve more bandwidth with WDM by transporting different wavelength data streams over a single optical fiber cable. In this way, Wavelength Division Multiplexing helps us maximize the fiber utilization factor and optimize our network investments.

What is CWDM?

CWDM is a type of WDM. Coarse Wavelength Division Multiplexing transmits a small number of channels. It operates with a broader gap of 20nm between channels. This wider channel spacing enables CWDM to be more resilient to temperature fluctuations. CWDM offers a maximum link distance of up to 60 kilometers, and it was standardized for 10-Gigabit Ethernet by the IEEE back in 2004. CWDM is known for its flexibility, as we can deploy it on various optical fiber networks. In telecom access networks and enterprise networks, CWDM is deployed to achieve point-to-point topology.

What is DWDM?

DWDM is a type of WDM. Dense Wavelength Division Multiplexing transmits a higher number of channels. It operates with a smaller gap of 0.8 nm or 0.4 nm between channels for 100 GHz or 50 GHz grids, respectively. The tighter spacing between channels makes DWDM capable of operating with a higher channel count than CWDM.
Another benefit of DWDM over CWDM is the possibility of amplification, making it an ideal choice for long-haul applications. While operating in a 50 GHz configuration, DWDM can accommodate up to 80 channels, each carrying 2.5 Gbps. An unamplified DWDM link can provide a maximum link distance of 80 kilometers. Whereas long-haul DWDM links of up to 1000 kilometers are achievable with amplification.

CWDM vs DWDM – What makes them different?

As discussed earlier, both CWDM and DWDM are Wavelength Division Multiplexing technologies. We use these two technologies to achieve the transmission of multiple signals carrying different types of data over a single fiber. CWDM and DWDM are very popular and considered practical tools to cater to increasing bandwidth demands. However, there are some differences between them, and now we will discuss the most common ones!

 Channel Spacing

In Wavelength Division Multiplexing, Channel Spacing can be defined as the wavelength difference between any two optical channels traveling adjacently.

With a wider spacing than DWDM; thus, it can accommodate fewer wavelengths. More precisely, in CWDM, we can have a maximum of 18 optical channels with a channel spacing or gap of 20nm.
On the other hand, DWDM operates with a much narrower spacing between optical channels. This narrower spacing of 0.8nm (for 100 GHz grid) and 0.4nm (for 50 GHz grid) enables Dense Wavelength Division Multiplexing (DWDM) technology to handle up to 160 wavelengths. In typical scenarios, wavelengths from C-band (1525nm to 1565nm) are utilized in DWDM systems except for some systems that can handle wavelengths from L-band (1570nm to 1610nm).

Transmission Distance

CWDM is designed for short-range communications, whereas DWDM is considered for long-range communications. In CWDM systems, the channel spacing of 20nm in the 1470 to 1610nm spectrum restricts amplification, and thus, it can provide a maximum link distance of up to 80km only. On the other hand, as discussed earlier in DWDM systems, light streams of different wavelengths travel at a much lower channel spacing. In other words, in DWDM systems, many optical channels operate in a dense environment. Without amplification, a DWDM system can offer a maximum link distance of up to 120km. The entire C-band spectrum being utilized by a DWDM link can be amplified cost-effectively. With attenuation, a DWDM link can be optimized to suit many long-haul applications where links stretch across hundreds of miles.

Optical Modulation

CWDM and DWDM differ in terms of optical modulation. In CWDM, optical modulation employs electronic tuning rather than a cooled laser. Conversely, in DWDM, optical modulation utilizes a cooled laser, with tuning dependent on temperature. While a cooled laser offers superior performance, a longer lifespan, and enhanced safety, it does come at the cost of relatively higher power consumption.

Cost Factor

In terms of cost, CWDM generally offers a more cost-effective solution in contrast to DWDM. There are many contributing factors related to this cost disparity but the most significant one is the different type of optical components they use. In DWDM system, complex cooled lasers are used resulting in higher manufacturing and operating cost. As far as the installation and maintenance is concerned, CWDM systems are simple to install and maintain than the DWDM systems. However, it's important to note that the cost difference should be evaluated based on the specific network requirements.

Advantages and Disadvantages

As discussed earlier, the primary difference between CWDM and DWDM is the channel spacing in these two technologies. CWDM operates with around 100 times wider channel spacing than DWDM. The factor of channel spacing, along with some other factors, results in attributing specific cons and pros in various terms such as cost, performance, link distance, etc. Let us discuss some of the main cons and pros related to CWDM and DWDM.

CWDM Pros and Cons

Pros

• it consumes less power
• it requires less space
• It can use both single-mode as well as multimode optical fiber
• It can use Lasers or LEDs for power
• It works with cheaper and smaller wave filters
• It costs less and gets you going with less investment

Cons

• It offers less capacity than DWDM
• It has less range
• Amplification is not possible
• Limited scalability is a drawback of CWDM

DWDM Pros and Cons

Pros

• It offers better capacity
• With EDFA`s, DWDM can provide hundreds of kilometers of coverage
• Amplification is possible
• DWDM offers better scalability options
• It offers more reliable data transmission over extensive distances

Cons

• It requires more space
• It requires more power
• It can only work with high-accuracy wave filters and lasers
• EDFA`s are expensive
• Its deployment costs are way more than CWDM
• Installation and maintenance of DWDM systems can be complex

Conclusion

CWDM and DWDM are two distinct optical communication technologies with their own sets of advantages and disadvantages.

Choose CWDM When:

• Power efficiency and space-saving are essential considerations.
• Your network operates on a smaller scale or a tighter budget.
• Amplification is not required, and you're working within a shorter range.

Choose DWDM When:

• High capacity and long-distance coverage are critical requirements.
• Your network demands extensive amplification capabilities.
• You can allocate more physical space and power resources to the network.
• Precision and accuracy in wave filters and lasers are non-negotiable.

Ultimately, the choice between CWDM and DWDM depends on your specific network needs, budget constraints, and performance expectations. Carefully evaluate these factors to determine the most suitable technology for your optical communication infrastructure.