In the field of optical fiber communications, wavelength division multiplexing (WDM) technology is a key means of increasing optical fiber transmission capacity. As a key offshoot of WDM technology, CWDM (Coarse Wavelength Division Multiplexing) has been widely used in specific scenarios due to its low cost and ease of deployment. Below, ETU will provide a detailed analysis of CWDM, including its definition, operating principles, key characteristics, wavelength planning, application scenarios, advantages, and limitations.

Ⅰ. Definition and Core Principles of CWDM

1. Definition

CWDM is a technology that multiplexes optical fiber bandwidth by simultaneously transmitting multiple optical signals of different wavelengths through a single optical fiber. Compared to dense wavelength division multiplexing (DWDM), its wavelength spacing is coarser (typically 20nm), hence the name "coarse wavelength division multiplexing."

2. Working Principle

The core principle of the CWDM system is wavelength division multiplexing:

2) Transmission process: Optical signals of different wavelengths propagate independently in the optical fiber without interfering with each other;

3) Receiving end: The mixed optical signal is separated by wavelength through a demultiplexer (DEMUX) and transmitted to the corresponding receiving device.

Simply put, CWDM is equivalent to "opening up multiple lanes" for optical fiber. Each "lane" corresponds to a wavelength and can carry different business signals (such as data, voice, video, etc.) at the same time.

Ⅱ. Key Characteristics of CWDM

1. Working Window

CWDM mainly operates in the optical fiber low-loss window of 1270nm-1610nm, covering the O -band (1260-1360nm), E-band (1360-1460nm), S-band (1460-1530nm), C-band (1530-1565nm) and L-band (1565-1625nm).

2. Channel Count

Due to the wide wavelength spacing and limitations of optical fiber loss and device characteristics, the maximum number of channels in a CWDM system is usually 16 ( some simplified systems can support 8 or 4 channels).

3. Transmission Distance

The transmission distance of CWDM systems is relatively limited, typically 20-80 kilometers (without repeaters). Extending the distance can be achieved by adding optical amplifiers (such as EDFAs) or dispersion compensation modules, but this increases costs.

4. Device Characteristics

1)  Laser: There is no need to use high-precision temperature-controlled lasers ( usually required for DWDM). Some can use lower-cost uncooled lasers to reduce power consumption and costs.

2) Filters: The requirements for wavelength selectivity are lower, and the manufacturing difficulty and cost of combiners/demultiplexers are significantly lower than those of DWDM devices.

Ⅲ. CWDM Wavelength Planning (ITU-T G.694.2 Standard)

The International Telecommunication Union (ITU-T) specifies the wavelength range of CWDM in the G.694.2 standard, defining 16 standard wavelengths, as follows:

As a professional module manufacturer, ETU-Link can provide 1G-800G optical modules. The following are several CWDM wavelength optical modules from ETU-Link :

Ⅳ. Application Scenarios of CWDM

Leveraging its low-cost and easy-to-deploy advantages, CWDM is primarily applied in scenarios with moderate transmission capacity and distance requirements:

1. Metropolitan Area Networks (MANs) and Access Networks

1) Applicable to the interconnection between various computer rooms and base stations in the city, and transmission of data, voice and other comprehensive services;

2) Supports the expansion of backbone links of enterprise networks and campus networks to meet the needs of multi-service aggregation.

2. Data Center Interconnect (DCI)

1) Connect different data centers over short distances (e.g., 10-40 kilometers) to achieve high-speed data transmission between servers and storage devices;

2) Supports multiplexing transmission of multiple protocol signals such as Ethernet (10G/40G/100G) and FC (Fibre Channel).

3. Cable Television (CATV) Networks

It is used for the transmission and distribution of broadcasting and television signals, while carrying video, broadband and other services, improving the utilization rate of optical fibers.

4. Industrial Control and Monitoring

In scenarios such as industrial parks and transportation hubs, long-distance transmission of surveillance videos and control signals is achieved, simplifying wiring.

Ⅴ. Advantages and Limitations of CWDM

1. Advantages:

Low Cost: Components (lasers, filters, etc.) do not require high-precision control, and the manufacturing cost is only 1/3-1/5 of DWDM. System deployment and maintenance are simple, reducing labor costs.

Flexible Deployment: Supports hot plugging and can gradually increase channels according to business needs (such as expanding from 4 waves to 8 waves and 16 waves); has low requirements for fiber type, and can use ordinary G.652 fiber without the need for dedicated fiber.

Low Power Consumption: Using uncooled lasers, the power consumption is significantly lower than that of DWDM cooled lasers.

Strong Compatibility: compatible with multiple rates (100M/1G/10G/40G) and protocols (Ethernet, SDH, FC, etc.), adapting to mixed business transmission.

2. Limitations:

Limited Capacity: The maximum number of channels is 16, which is far lower than the hundreds of channels of DWDM and is not suitable for ultra-large backbone networks.

Short Transmission Distance: The transmission distance without repeaters is usually no more than 80 kilometers, while DWDM can support thousands of kilometers of transmission through amplifiers.

Low Wavelength Utilization: The wide interval of 20nm results in low fiber bandwidth utilization, which is not suitable for scenarios with extremely high bandwidth density requirements.

Ⅵ. Summary

As a cost-effective wavelength division multiplexing technology, CWDM offers irreplaceable advantages in low- to medium-capacity, short- to medium-distance communication scenarios. Its low cost and ease of deployment meet the bandwidth requirements of metropolitan area networks, access networks, and data center interconnection scenarios, making it an ideal choice for balancing performance and cost.

With the development of optical communication technology, CWDM is also constantly evolving (such as supporting higher-speed 100G CWDM) and will continue to play an important role in small and medium-sized networks and edge computing scenarios in the future.

About ETU-LINK

ETU-Link Technology Co., Ltd., founded in 2014, is a high-tech enterprise specializing in the research, development, production, and sales of optical communication components. With high-speed optical modules as its core product, the company specializes in serving the fiber optic communication markets, including telecommunications, data communications, and storage.