CWDM stands for Course Wavelength-Division Multiplexing.
The CWDM method multiplexes optical signals together on one single fiber. To achieve this it uses different colors (wavelengths) which are combined in a MUX. The device where the optical signals are multiplexed and de-multiplexed is called a MUX or a fiber optical multiplexer or a CWDM multiplexer. In most cases these MUXES are passive so no electricity is needed, hence the meantime between failures is about 500 years.
All optical transmission is done by dual fibers where one fiber is transporting data from east to west and the other west to east. This dual function is possible because one MUX has both a multiplexer and a de-multiplexer. There are two standards for multiplexing: CWDM and DWDM. The main difference is the wavelength steps between the channels: for CWDM this is 20nm (course) and for DWDM this is typically 0.8nm (dense). CWDM has 18 wavelengths from 1610 to 1270 with steps of 20nm.
The top eight wavelengths (1610-1470) are the most used and also are not affected by what is referred to as "the waterpeak". This waterpeak causes high attenuation from wavelengths 1370-1410nm on old types of fibers. Solid Optics offers the Passive CWDM MUX in 8 port and 18 ports and we also have the full range of CWDM 1G (24dB/32dB/37dB) and SFP+/XFP 10G ER/ZR optics in stock. All of our CWDM MUXES have the MUX and DEMUX inside and come in a 19 inch chassis with rack mounts.