CWDM stands for Course Wavelength Division Multiplexer. CWDM’s work similar to the WDM’s explained in questions 1 and 2. “Course” meaning the channel spacing is 20nm with a working channel passband of +/-6.5nm from the wavelengths
center. This is tighter channel spacing than typical Wide Band Optic (WBO) WDM’s, which allows for more channels within the ITU CWDM grid. CWDM’s allow you to multiplex or demultiplex multiple wavelengths over one fiber. This is done by using light wavelength filters.
The filters only allow specific wavelengths of light to pass through the filter to a single fiber port and the remainder of the wavelengths are then reflected back to another separate fiber port. When used in a series or concatenated together this allows you to add multiple wavelengths on to one fiber. From 1270nm to 1610nm there are 18 individual wavelengths/channels separated by 20nm spacing.
