This application note describes how to upgrade a 1310nm single wavelength network by adding CWDM wavelengths using passive mux/demux equipment, allowing for increased bandwidth without significant costs. The solution is flexible, enabling the addition of up to 8 CWDM wavelengths, and can also be adapted for 1550nm networks. Furthermore, it outlines the potential for future expansion using DWDM technology, thereby accommodating even greater bandwidth needs.