LWDM and CWDM for QSFP28 100G Optical Transceiver

What are LWDM and CWDM?

This refers to the category of 100G optical modules (4*25G). The main difference is the wavelength selection during 100G four-wavelength wavelength division multiplexing. There are two commonly used wavelength categories.

The first is dense wavelength division multiplexing, which uses the LAN WDM wavelength defined by 802.3, abbreviated as LWDM, and is mainly used in the 10km 100GBASE-LR4 category. These standards were originally defined for the telecom client side.

The second is coarse wavelength division multiplexing. The selected 20nm wavelength interval, abbreviated as CWDM, is mainly used in 2km data centers. We also know that the application of 100G optical modules in data centers is comparable to telecom applications, so the CWDM industry chain is very mature, and its wavelength selection has become a mainstream solution

100G LAN WDM, according to the previous distance classification, does not have the 2km range, because the LAN metropolitan area network rarely uses this distance, only SR short distance, LR long distance, etc., but look at the picture above, the data center With the rapid development of 802.3, the distance of 802.3 has increased the subdivision distance of 500 meters and 2km of DR4 and FR4 in addition to SR4, LR4 (10km).

For the deployment of data centers, there are 100 meters, 500 meters, and 2km. These subdivision distances. Although the MSA organization is not a standard organization, the market is huge. They formulated the application of CWDM4, 2km, and then added the 10km indicator.

In short, the two began to gradually merge in distance, but the wavelength still needs to be distinguished.