Optical multi-demultiplexer

An optical multi-demultiplexer comprising:

• 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 provided between the input waveguide and the output waveguides and including a plurality of channel waveguides having different waveguide lengths;
• an input slab waveguide formed between the input waveguide and the arrayed waveguide, said input slab waveguide including a core layer and a clad layer;
• an output slab waveguide formed between the arrayed waveguide and the output waveguides, said output slab waveguide including a core layer and a clad layer, and
• two or more island regions having a refractive index different from that of the core layers of the input and output slab waveguides are provided in at least one of the slab waveguides and situated in positions associated with the channel waveguides of the arrayed waveguide.