Optical communications system, branching ratio determination method, and transmission distance determination method

A split ratio determination method of determining a split ratio of an uneven-split optical splitter for an optical communication system, the optical communication system including

• an uneven-split optical splitter in which m−1 2×2 fiber-optic splitters are combined and connected between m primary ports and m secondary ports (where m is an integer equal to or greater than 2),
• an optical line terminal that inputs and outputs optical signals of different wavelengths with respect to the 1st and 2nd primary ports of the uneven-split optical splitter, or inputs and outputs a wavelength-multiplexed optical signal with respect to one of the 1st and 2nd primary ports, and
• an optical network unit that inputs and outputs optical signals of a single wavelength or wavelength-multiplexed optical signals with respect to each of the secondary ports of the uneven-split optical splitter, wherein in the uneven-split optical splitter,
• the two inputs of the fiber-optic splitter in a 1st stage are connected to the 1st and 2nd primary ports, and one of the two outputs is connected to the 1st secondary port,
• one of the two inputs of the fiber-optic splitter in a kth stage (where k is an integer equal to or greater than 2 and equal to or less than m−2) is connected to the (k+1)th primary port while the other of the two inputs is connected to one of the two outputs of the fiber-optic splitter in a (k−1)th stage, and one of the two outputs is connected to the kth secondary port,
• one of the two inputs of the fiber-optic splitter in a (m−1)th stage is connected to the mth primary port while the other of the two inputs is connected to one of the two outputs of the fiber-optic splitter in a (m−2)th stage, and the two outputs are connected to the (m−1)th and mth secondary ports,
• the split ratio determination method comprising:
• detecting, for each secondary port other than the 1st secondary port, a maximum distance between the optical network unit farthest from the optical line terminal and the optical line terminal;
• computing a split ratio by wavelength for each fiber-optic splitter by substituting the maximum distance into a function of the split ratio of the fiber-optic splitter, the maximum distance, and the wavelength;
• and
• finding a melt-draw distance for each fiber-optic splitter by which the computed split ratios for each wavelength are achieved at the same time,
• where the fiber-optic splitter in the (m−1)th stage exists in a case where m is 3 or greater, and the fiber-optic splitter in the kth stage exists in a case where m is 4 or greater.