OPTICAL MULTIPLEXER/DEMULTIPLEXER AND METHOD FOR MULTIPLEXING/DEMULTIPLEXING LIGHT BEAM

PROBLEM TO BE SOLVED: To provide, for example, a compact integrated optical multiplexer/demultiplexer having an improved efficiency of optical coupling with an outer optical element and an improved tolerance of coupling efficiency for displacement without increasing the size.SOLUTION: An optical multiplexer/demultiplexer comprises: an optical multiplexing/demultiplexing part that multiplexes a plurality of light beams having different wavelengths into wavelength multiplex light or that demultiplexes wavelength multiplex light into a plurality of light beams having different wavelengths; a plurality of multimode optical waveguides that optically connect to and between a plurality of optical elements and the optical multiplexing/demultiplexing part and that have lengths corresponding to each of the different wavelengths and guide the plurality of light beams in multimode, and a single multimode optical waveguide that optically connects to and between one optical element and the optical multiplexing/demultiplexing part, that has a length corresponding to the different wavelengths, and that guides the wavelength multiplex light in multimode.