In an arrayed waveguide grating type wavelength division demultiplexer including
an input waveguide, an input slab waveguide, a phase-grating waveguide array composed
of a plurality of optical channel waveguides, an output slab waveguide, and a plurality
of output waveguides provided in a core layer so as to form a predetermined pattern,
the input slab waveguide is configured to have portions with locally varied thickness
in at least the core layer or 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. With this arrangement of the device, the device can be applied to a case
where it is undesirable to dope materials of Ge, Ti and Ce. Moreover, with this
arrangement of the device, it becomes possible to avoid deterioration with time
passage and reduce polarization dependent loss, thereby to improve optical coupling loss.
