WDM PONs based on colorless technology

•WDM PONs will be introduced with applications in business and mobile fronthaul segments.•Fixed wavelength technologies will first be deployed such as CWDM dual fiber and CWDM single fiber.•When higher density of ports will be required, colorless technologies will be essential.•A WDM PON system based on self-seeded RSOAs is experimented with CPRI3 links.•Good performances demonstrated with long reach and coexistence with legacy PONs.