Wavelength-division multiplexing - Wikipedia
https://en.wikipedia.org/wiki/Wavelength-division_multiplexing
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light.
WDM Basics: Understanding Wavelength Division... | FS Community
https://community.fs.com/blog/do-you-know-all-these-terminologies-of-wdm-technology.html
WDM (Wavelength Division Multiplexing) technology is an ideal solution to get more bandwidth and lower cost in nowaday telecommunications networks.