CWDM vs. DWDM: Understanding the Differences

WDM is a technology that increases the capacity of optical fiber communication by transmitting multiple optical signals of different wavelengths in the same optical fiber. Based on wavelength spacing and application scenarios, WDM technology can be divided into two main categories: CWDM and DWDM.

1. What is CWDM?

CWDM is a technology that achieves optical fiber bandwidth multiplexing by simultaneously transmitting multiple optical signals of different wavelengths in a single optical fiber. Compared to DWDM, its wavelength spacing is coarser, hence the name "coarse wavelength division multiplexing."

At the transmitting end, the multiplexer combines multiple optical signals of different wavelengths into a single optical fiber for transmission; during transmission, the different wavelengths of optical signals are transmitted independently in the fiber without interference; at the receiving end, the demultiplexer separates the mixed optical signals according to wavelength and transmits them separately to the corresponding receiving devices.

2. What is DWDM?

Dense wavelength division multiplexing is a high-density wavelength division multiplexing technology, also known as dense wavelength division multiplexing. DWDM (Digital Wavelength Distributed) is a technology used in fiber optic transmission systems. It leverages the broadband characteristics of optical fibers to combine multiple optical signals into a single fiber for transmission. By simultaneously transmitting multiple signals of different wavelengths within the same fiber, it significantly improves fiber utilization.

DWDM technology utilizes the bandwidth and low-loss characteristics of single-mode fiber, employing multiple wavelengths as carriers, thus allowing the simultaneous transmission of various carrier channels within the fiber.

Based on transmission distance, DWDM can be divided into long-distance DWDM and short-distance DWDM. Long-distance DWDM can support transmission distances of hundreds of kilometers or even longer, while short-distance DWDM is suitable for data transmission over small areas.

Based on the number of light waves, DWDM can be divided into single-channel DWDM and multi-channel DWDM. Single-channel DWDM transmits one light wave, while multi-channel DWDM can transmit multiple light waves simultaneously.

They are also classified into C-band and L-band. The C-band is suitable for long-distance transmission, while the L-band is suitable for short-distance transmission.

Based on the application scenario, optical communication is divided into optical communication and optical transmission. The former is suitable for high-speed data transmission in data centers and the internet, while the latter is suitable for remote control and monitoring in fields such as power, transportation, and broadcasting.

3. What are the types of CWDM and DWDM optical modules?

CWDM SFP optical modules are optical modules that use CWDM technology and are packaged as SFPs. They are widely used in 100Mbps Ethernet, Gigabit Ethernet, 1G/2G/4G Fibre Channel, and synchronous optical networks. They transmit over single-mode fiber at wavelengths of 127-1610nm, with a maximum transmission distance of 20 to 120km.

10G CWDM SFP+ optical modules use CWDM technology to combine different wavelengths together for transmission over a single-mode fiber, thus saving fiber resources. They adopt a hot-pluggable SFP+ package, operate at wavelengths of 1271-1611nm, and are widely used in 10G Ethernet, optical transport networks, and 10G CPRI base station fronthaul. They are also compatible with synchronous optical networks and 10G Fibre Channel, with a maximum transmission distance of 10 to 80km.

The 25G CWDM SFP28 optical module uses a hot-pluggable SFP28 package, transmits data via single-mode fiber, has a maximum transmission rate of 25G, and is used in 25G Ethernet and 5G fronthaul networks, with a maximum transmission distance of 10 to 40 km.

The 40G CWDM QSFP+ optical module uses a QSFP+ package, transmits data via single-mode fiber, has a maximum transmission rate of 40G, and a maximum transmission distance of 30 to 40 km.

The 100G CWDM QSFP28 optical module uses the QSFP28 package standard, supports data transmission rates up to 100G, and is suitable for high-capacity data transmission and processing needs.

DWDM SFP optical modules utilize DWDM technology and are packaged in SFP. The DWDM SFP series includes 44 selectable channels, supporting speeds up to 100Mbps. They are widely used in 100Mbps Ethernet, Gigabit Ethernet, 1G/2G Fibre Channel, and synchronous optical networks. Operating wavelengths range from 1528.77nm to 1563.86nm, with a wavelength spacing of 0.8nm, they can transmit over single-mode fiber at distances of 80km to 120km.

10G DWDM SFP+ optical modules use hot-pluggable SFP+ packages, support the entire C-band, and offer commercial-grade (0℃-70℃) and industrial-grade (-40℃-85℃) operating temperature ranges. They comply with SFP28 MSA and 10G Ethernet standards, and can transmit over single-mode fiber at distances of 40km to 80km.

The 25G DWDM SFP28 optical module is primarily used to meet the needs of 25G Ethernet and 5G fronthaul services, with a maximum speed of up to 25.78Gbps. Its operating wavelength is 1528.77nm-1563.86nm, with a wavelength spacing of 0.8nm. The maximum transmission distance through single-mode fiber is 10km.

4. What are the application areas of CWDM and DWDM optical modules?

CWDM technology can effectively expand the interconnection between various data centers and base stations within a city, supporting the expansion of backbone links in enterprise networks and campus networks, and data center interconnection.

DWDM technology can effectively expand the connection between data centers, making data transmission faster and more reliable. It supports remote data backup and disaster recovery, thereby ensuring data security and reliability. It can help cloud computing provide better management and optimization, thereby improving performance and reliability. It can expand the capabilities of telecommunications and broadband services, providing higher speeds and greater bandwidth. It can help hospitals and medical institutions provide better management and telemedicine services, thereby improving medical efficiency and quality.

5. What are the differences between CWDM and DWDM?

5.1 Different Wavelength Spacing

CWDM has a wider carrier channel spacing, with a spacing of 20 nm per band. Only about 8 to 16 wavelengths can be multiplexed on the same fiber. DWDM has a relatively narrower carrier channel spacing, with spacings of 0.2 nm, 0.4 nm, 0.8 nm, and 1.6 nm per band, allowing for the multiplexing of 80 to 160 wavelengths.

5.2 Different Wavelength Ranges

CWDM operates in the wavelength range of 1270 nm to 1610 nm, while DWDM operates within a specific portion of the CWDM wavelength range, specifically 1525 nm to 1565 nm (C-band) and 1570 nm to 1610 nm (L-band).

5.3 Different Device Costs

CWDM modulated lasers use uncooled lasers, while DWDM uses cooled lasers. Cooled lasers employ temperature tuning, while uncooled lasers use electronic tuning. Due to the highly uneven temperature distribution across the wavelength range, temperature tuning is more difficult to achieve and therefore more expensive.

5.4 Application Differences

DWDM optical modules can perform long-distance, high-capacity transmission tasks in long-distance backbone networks. They are used in some high-capacity metropolitan area network (MAN) core nodes, telecom 5G, MANs, backbone networks, and some data centers. CWDM optical modules are mainly used in MAN access layers, enterprise networks, and campus networks.