Arrayed waveguide grating type wavelength division demultiplexer

An arrayed waveguide grating type wavelength division demultiplexer having a waveguide grating array which is composed of a substrate, a cladding layer provided on the substrate and a core layer provided in the cladding layer so as to form a predetermined pattern, comprising:

• an input waveguide for propagating a plurality of input light beams having respective wavelength, each beam being associated with one of a plurality of optical channel waveguides;
• an input slab waveguide for allowing a free propagation of the light beams from the input waveguide;
• a phase-grating waveguide array composed of a plurality of optical channel waveguides for propagating the light beams from the input slab waveguide, each of the optical channel waveguides having a waveguide length different from one another by a predetermined length;
• an output slab waveguide for allowing a free propagation of the light beams from the plurality of optical channel waveguides of the phase-grating waveguide array, and focusing the light beams at a different position depending on the wavelength of the light beams;
• and
• a plurality of output waveguides for propagating the light beams focused by the outputs lab waveguide, respectively, wherein
• the input waveguide, the input slab waveguide, the phase-grating waveguide array, the output slab waveguide, and the plurality of output waveguides are provided in the core layer so as to form the predetermined pattern, and
• the input slab waveguide is configured to have portions with locally varied thickness in at least one of the core layer and the cladding layer at the vicinity of each coupling portion of the optical channel waveguide depending on the layout of the optical channel waveguides, whereby the input slab waveguide is made to have a high refractive index region having a refractive index relatively higher than surrounding regions thereof at the vicinity of each coupling portion of the optical channel waveguide.