Classification of WDM

CWDM (Coarse WDM) rarefaction wavelength division multiplexing

Due to the limited technical conditions in the early days, the wavelength interval will be controlled to several tens of nm, which is a relatively scattered wavelength division multiplexing.

The wavelength interval of CWDM, a common example among types of WDM, is 20nm, the wavelength range is from 1270nm to 1610nm, and there are 18 wave bands.

At the beginning, the wavelength range of CWDM (ITU-T G.694.2) specified by the International Telecommunication Union (ITU) is from 1271 to 1611nm.

However, because the 1270-1470nm band has a significant increase in attenuation, many old-type optical fibers cannot be used normally, CWDM generally preferentially uses the 8 bands from 1470 to 1610nm.

DWDM (Dense WDM) dense wavelength division multiplexing

The wavelength interval is getting shorter and shorter to the level of a few nm, so it becomes a compact WDM-DWDM.

The DWDM wavelength interval can be 1.6nm, 0.8nm, 0.4nm, 0.2nm, which can accommodate 40, 80, 160 waves (can support 192 waves at most). The wavelength range of DWDM is 1525nm to 1565nm (C band) and 1570nm to 1610nm (L band).

DWDM commonly uses C band, wavelength interval is 0.4nm, and channel frequency interval is 50GHz

MWDM Metro Wave Division Multiplexing

This was proposed by China Mobile with the active fronthaul solution (also known as Open WDM) in June 2019.

MWDM reuses low-cost DML optical chips for the first 6 waves of the 25G CWDM industry chain, and rapidly advances the 12-wavelength WDM system, which greatly saves precious resources of fronthaul optical fiber and adapts to the current urgency of 5G commercial use.

The current network pilot of the MWDM semi-active 5G fronthaul solution strongly supports the maturity of MWDM technology and will accelerate the commercialization of the semi-active 5G fronthaul solution.

5G fronthaul requires at least 12 wavelength channels, so the three major telecom operators' plans all aim at achieving 12 wavelengths, exploring various types of WDM to meet this demand.

By increasing TEC (Thermal Electronic Cooler, semiconductor cooler) temperature control, there are left and right shifts of the 3.5nm wavelength, forming 12 wavelengths.

This solution not only reuses the CWDM industry chain, but also meets China Mobile's own 10km fronthaul distance requirements, while also saving a lot of optical fiber resources, which can be described as multi-tasking.

LWDM

LWDM is based on the Ethernet channel wavelength division multiplexing (LAN WDM), and some people call it fine wavelength division multiplexing.

It is expanded from the existing 8 waves to 12 waves according to the channel interval of 800GHz.

DML refers to the Directly Modulated Laser at the TOSA transmitting end of the optical module, which corresponds to EML (Electlro-absorption Modulated Laser). EML costs more. PIN refers to the diode at the receiving end of the optical module ROSA.