Patent ID: 6920264

Claim:
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 wavelengths; an input slab waveguide for allowing a free propagation of the light beams from the input waveguide; a phase-grating waveguide array comprising 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, and each optical channel waveguide having a coupling portion coupling the respective optical channel waveguide to the input slab waveguide; 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 output slab 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 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.