Optical network system and optical communication method

An optical communication method executable by an optical network system that includes an optical line terminal, an optical splitter that is connected to the optical line terminal via one first optical fiber, and a plurality of optical network units that are connected to the optical splitter via respective second optical fibers, the optical communication method comprising:

• respectively communicating, by the plurality of optical network units, with the optical line terminal using corresponding working wavelengths uniquely assigned to the plurality of optical network units;
• communicating, by the optical line terminal, with an optical network unit in the plurality of optical network units using a corresponding working wavelength that is assigned to the optical network unit and with a spare optical network unit in the plurality of optical network units using a spare wavelength through which all of the plurality of optical network units are able to receive an optical signal when a failure has occurred in communication using the working wavelength;
• and
• transmitting, by the optical network unit that is connected to the optical splitter, to the optical line terminal a wavelength number that indicates the working wavelength to be replaced with the spare wavelength before an operation of a communication between the optical network unit and the optical line terminal is switched from an operation using the working wavelength to an operation using the spare wavelength.