A so-called WDM is a wavelength-selective coupler. The optical frequency multiplexing method, wavelength division multiplexing (WDM), splits the wavelengths in such a way that each spectral color has its own transmission channel.
Optimized MM WDMs for 850 nm and 1310 nm
Multi-mode WDMs are usually optimized for the two wavelengths: 850 nm and 1310 nm. They permit bidirectional and unidirectional operation.