To provide an arrayed-waveguide diffraction grating, an optical communication device, and an optical communication system.

The optical communication system 10 of this invention includes: a station side device 12 for sending a wavelength multiplex-modulated data to an optical communication link; a wavelength demultiplexer 16 for receiving the wavelength multiplex-modulated data from the station side device 12 and demultiplexing the data; and two or more user devices 18 for forming an optical network routed by the wavelength demultiplexer 16. The wavelength demultiplexer 16 used in this invention includes the optical communication device including a circulating arrayed-waveguide diffraction grating and enables full mesh connection for equivalently connecting all the user devices.