With the explosion of digital traffic and the ever-growing array of bandwidth-hungry applications, the demand of extending the capacity of each wavelength and lowering the cost per bit in the network is required. The WDM has been proved to be the more cost-effective technology.

Wavelength-division multiplexing (WDM) technology combines multiple signals onto the same fiber by using different wavelengths (colors), each optical channel can carry any transmission format. There are two types of WDM architectures: CWDM - coarse wavelength division multiplexing, and DWDM - dense wavelength division multiplexing. Each solution has characteristics that suite different environments, networks and user requirements.