Disclosed is a wavelength-shifted bidirectional WDM optical network including: an optical line terminal including an optical line terminal (OLT) including a first optical transmitter transmitting a downstream WDM optical signal, a first high-density wavelength multiplexer/demultiplexer wavelength-multiplexing the downstream WDM optical signal or wavelength-demultiplexing a wavelength-multiplexed upstream WDM optical signal, and a first optical receiver receiving the wavelength-demultiplexed upstream WDM optical signal; a remote node (RN) including a second high-density wavelength multiplexer/demultiplexer shifting a center wavelength of the upstream WDM optical signal and wavelength-multiplexing the upstream WDM optical signal with the shifted center wavelength or wavelength-demultiplexing the wavelength-multiplexed downstream WDM optical signal; and multiple optical network units (ONUs) each including a second optical transmitter transmitting the upstream WDM optical signal and second optical receiver receiving the wavelength-demultiplexed downstream WDM optical signal.