Optical communication systems and optical communication abnormal return method

The present invention aims to provide an optical communication system and an optical communication abnormality restoration method in WDM / TDM-PON. Optical communication systems and optical communication abnormality return method according to the present invention, when a malfunction occurs in one of the transmission and reception of the wavelength of the optical line terminal of the PON system, the subscriber unit communicating with a certain wavelength, the wavelength of communicating advance It switched to the wavelength of another reserve that had been specified. Also, the station side device is also switched to communicate using a wavelength of the same called subscriber device.