Wavelength multiplexing with up to 18 wavelengths on 1 fibre.
Passive CWDM panels/modules are a reliable and reasonable method for transferring several wavelengths/signals over the same fibre. In this way you may increase the capacity of existing fibre-cable significantly. A big advantage of using passive wavelength multiplexing is also that the method is protocol- and bitrate independent.
A complete system with components for two-way communication (multiplexer and de-multiplexer) in both ends are made with two panels/modules.