What is CWDM?

What is WDM?

Wavelength-division multiplexing (WDM) technology combines multiple wavelengths into a single optical fiber. This technique enables better fiber utilization and increases fiber capacity. In WDM networks, each channel is transparent to the speed and type of data. Any mix of Ethernet, SAN, OTN, SONET/SDH and native video services are transmitted simultaneously over a single fiber or fiber pair.

There are two types of WDM technologies: DWDM - dense wavelength division multiplexing, and CWDM - coarse wavelength division multiplexing. Each technology has characteristics that suit different environments, networks and user requirements.

What is CWDM?

CWDM used to be the popular choice in low capacity, short distance and low rate (up to 10G per wavelength) applications, and in networks where the initial requirement is up to 16 wavelengths. The low cost entry point especially for 1G and 10G services and the difference in economic scale make CWDM ideal for initial low capacity network set up. However, CWDM reach is limited as it cannot be amplified and does not support tunable DWDM 100G/200G/400G wavelengths so becoming less and less common in new designs of optical networks.

CWDM networks typically transport 8 client interfaces over the same fiber. The large bandwidth of CWDM wavelengths and the spacing between them enable to expand the network between 1531nm and 1551nm.

How can DWDM technology upgrade a CWDM network?

When the network needs to be upgraded to support the increase in capacity requirements, DWDM wavelengths can be added to the existing CWDM infrastructure, essentially extending its life.

This achieves higher data transport capacity on the same fiber optic cable without the need to change existing fiber infrastructure between the network sites (Figure 1).

Mapping DWDM Channels in CWDM

Figure 1: Mapping DWDM Channels in CWDM

A single outgoing and incoming wavelength in an existing CWDM infrastructure is used for 8 DWDM channels multiplexed into the original CWDM wavelength (Figure 2).

Expansion is achieved with no interruption to the network services or data, and without the need to change or replace any of the working CWDM infrastructure.

Expansion using the DWDM spectrum

Figure 2: Expansion using the DWDM spectrum

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