A wavelength division multiplexed passive optical network (WDM PON) is disclosed. In one aspect, WDM-PON comprises a central office comprising a plurality of semiconductor optical amplifiers each adapted to output an optical signal modulated in accordance with data inputted thereto, and a wavelength division multiplexer adapted to multiplex the optical signals outputted from the semiconductor optical amplifiers, and a remote node connected to the central office via a main optical fiber, adapted to distribute the optical signals received, on to corresponding distribution optical fibers connected thereto, and a plurality of optical network units connected to the remote node via corresponding distribution optical fibers, the optical network units receiving from the remote node the optical signals associated therewith. In another aspect of the invention, the central office further comprises an amplifier for amplifying the multiplexed signal.