Wave division multiplexing (WDM) refers to an optical transmission technique where multiple optical signals are transmitted on a single optical fiber using diffe.rent wavelengths. In today's high-end WDM systems designed for long-distance communications, each optical signa (often referred to as a channel or a wavelength) can operate at up to  10 Gbps. Currently, available systems support from 4 to 64 channels . The term dense wave division multiplexing (DWDM) is often used to describe systems supporting a large number of channels, normally 16 or more.

Eoptolink DWDM system is a Cost-effective applications, through the use of a great number of optical channels on a single optical fibre pair. Granularity in the capacity with the possibility of adding new optical channels, also operating at different bit rates, to the same optical fibre pair, as additional capacity is required. Modularity in the reach of the systems, with possible link length from a few to more than one thousand kilometres. Flexibility in link configuration [linear, ring with or without optical add drop multiplexing (DWDM OADM). 100 GHz channel spacing (G.694.1). Up to forty 10 Gbit/s optical channels 100 GHz spaced per DWDM system, in C-band G.652, G.653, G.655 optical fibre-supported

Recommended standards:
G.694.1 "Spectral grids for WDM applications: DWDM frequency grid" specifies a frequency grid which supports a variety of DWDM channel spacings ranging from 12.5 GHz to 100 GHz (and wider)
G.696.1 "Longitudinally compatible intra-domain DWDM applications" specifies long-haul DWDM systems primarily intended for backbone applications
G.698.1 "Multichannel DWDM applications with single channel optical interfaces" specifies DWDM systems primarily intended for metro applications with channel bit rates up to 10 Gbit/s
G.698.2 "Amplified multichannel DWDM applications with single channel optical interfaces" specifies DWDM systems primarily intended for core metro/regional applications that include line optical amplifiers with channel bit rates up to 10 Gbit/s
G.959.1 "Optical transport networks physical layer interfaces" specifies DWDM optical systems with 32 channels for different bit rate classes up to 10 Gbit/s
G.973 "Characteristics of repeaterless optical fibre submarine cable systems" deals with submarine DWDM systems without line optical amplifiers
G.977 "Characteristics of optically amplified optical fibre submarine cable systems" deals with submarine DWDM systems with line optical amplifiers