100GBASECWDM4

100GBASE-CWDM4 is a 100 Gigabit Ethernet physical-layer specification that uses coarse wavelength-division multiplexing to carry four parallel 25 Gbps channels on four distinct wavelengths within the CWDM grid. The approach multiplexes four 25 Gbps NRZ channels onto a single optical fiber pair and demultiplexes them at the receiving end, yielding an aggregate data rate of 100 Gbps. The four wavelengths commonly cited for CWDM4 are around 1271, 1291, 1311, and 1331 nanometers, following the ITU-T CWDM grid (G.694.2).

The standard is typically implemented in pluggable transceiver modules in the QSFP28 form factor, enabling 100GBASE-CWDM4 links between switches, routers, or other optical devices. Each lane runs at about 25 Gbps, and the optics are designed for relatively short to medium reach over standard single-mode fiber. A common reach specification for CWDM4 is up to about 2 kilometers on standard SMF, though actual reach can vary with fiber quality, optics, and dispersion management. Forward error correction may be employed to improve link reliability and margin.

Compared with other 100G approaches such as 100GBASE-LR4 or 100GBASE-ER4, CWDM4 can offer lower cost and leverage existing CWDM infrastructure or vendor-friendly MSA ecosystem, but typically provides shorter reach and may be more sensitive to channel power balance and wavelength alignment. CWDM4 remains a practical option for data center interconnects and campus networks where moderate distances and multiplexed 100G transport are desirable.