The invention is related to the field of telecommunications, more specific to the sector of passive wavelength division multiplexed access systems (WDM-PON). The invention is WDM-PON access communication system with two different intensity modulation formats return-to-zero (RZ) and non-return-to-zero (NRZ), and an optical channel add-drop module in optical line section, which provides solution for a transmission system expansion and/or branching and adding of new subscribers or services with passive optical elements without conversion from optical to electrical signal. Such a solution is ready to be integrated into already existing optical access networks, thus providing opportunity to use two different types of optical signal intensity modulation formats and increase data rates and transmission distance between the service provider and the client.