An optical multi-demultiplexer of the present invention comprises an input waveguide
to which wavelength division multiple signals are applied, a plurality of output
waveguides for demultiplexing and outputting the wavelength division multiple signals,
an arrayed waveguide including a plurality of channel waveguides having different
waveguide lengths, an input slab waveguide, and an output slab waveguide. The input
slab waveguide is provided between the input waveguide and the arrayed waveguide.
The output slab waveguide is provided between the arrayed waveguide and the output
waveguides. The input slab waveguide is formed with tapered island regions having
a refractive index lower than that of the core layer of the slab waveguide. The
island regions are situated in positions opposite the channel waveguides of the
arrayed waveguide.
