To provide a small-sized optical multiplexing demultiplexing element which is free of wavelength absence.
The optical multiplexing demultiplexing element has a plurality of input/output waveguides 1 to 11, an array waveguide 14 comprising a plurality of waveguides differing in length, a slab waveguide 12 which has one-end sides of the input/output waveguides 1 to 11 connected to one end surface and one end of the array waveguide 14 connected to the other end surface, and a high-reflection film 15 to which the other end of the array waveguide 14 is respectively connected. The input/output waveguides 1 to 11 each comprises an input waveguide on which wavelength multiplex signal light having a specified wavelength band is made incident and a waveguide other than the input waveguide and an output waveguide group which comprises output waveguides other than the input waveguide such that the wavelength multiplex light is separated by wavelengths by the slab waveguide 12 and converged on end surface of the respective waveguides; and the wavelength of light which is converged on an end surface of a waveguide adjacent to both the sides of the input waveguide is set to the wavelgnths on both the ends of the specified wavelength band.
Katsuhiro Ito
Ishibashi Masayuki