An integrated optical circuit comprising an optical waveguide and an
evanescent coupler. The optical waveguide is located on a wafer. The
optical waveguide is formed from an upper semiconductor layer of the
wafer, a gate oxide layer deposited on the upper semiconductor layer, and
a polysilicon layer deposited on the gate oxide layer. The evanescent
coupling region is formed at least in part from a gap portion that
optically couples light to the upper semiconductor layer of the optical
waveguide using the evanescent coupling region. Light can be coupled from
outside of the passive optical waveguide device via the evanescent
coupling region into the optical waveguide. Alternatively, light can be
coupled from the optical waveguide through the evanescent coupling region
out of the passive optical waveguide device. The polysilicon layer
projects a region of static effective mode index within the optical
waveguide, wherein the region of static effective mode index has a
different effective mode index than the optical waveguide outside of the
region of static effective mode index. The value and position of the
effective mode index within the region of static effective mode index
remains substantially unchanged over time and applies a substantially
unchanging optical function to light travelling through the region of
static effective mode index within the optical waveguide over the lifetime
of the passive optical waveguide device.
