Optical communication system and optical communication method

An optical communication system of a passive optical network (PON) in which an optical path is laid in a ring topology, the optical communication system comprising:

• a termination device, which is referred to as an optical line terminal (OLT), connected to the optical path so that an optical signal output is transmitted on the optical path in at least one of a clockwise direction or a counterclockwise direction;
• one or more unequal branch optical splitters having one primary-side main port, one secondary-side main port, a plurality of primary-side branch ports, and a plurality of secondary-side branch ports and connected to the optical path via the primary-side main port and the secondary-side main port, the one or more unequal branch optical splitters configured to branch the optical signal transmitted clockwise from the optical path, output optical signals obtained by branching from the respective secondary-side branch ports at a predetermined branching ratio, branch the optical signal transmitted counterclockwise from the optical path, and output optical signals obtained by branching from the respective primary-side branch ports at a predetermined branching ratio;
• and
• a network device, which is referred to as an optical network unit (ONU), connected to one primary-side branch port of the plurality of primary-side branch ports and a secondary-side branch port of the plurality of secondary-side branch ports corresponding to the one primary-side branch port in the unequal branch optical splitter.