Patent ID: 8218932

Claim:
A polarization independent optical device in which an optical element is formed on a major surface of a substrate, the optical element including a first clad, a second clad, and a core sandwiched between the first and second clads, the core comprising: a planar waveguide layer having a first surface in contact with the first clad, a second surface in contact with the second clad, and a thickness measured from the first surface to the second surface; and a plurality of ridges protruding from the second surface of the planar waveguide layer into the second clad to form a ridge waveguide structure for guiding propagation of light in the core, the ridges being integral with the planar waveguide layer; wherein the ridges have a rectangular cross section in a plane orthogonal to a direction of the propagation of the light through the core, the rectangular cross section having constant dimensions including a ridge width measured parallel to the second surface of the planar waveguide layer and a ridge height measured from the second surface of the planar waveguide layer to respective tops of the ridges, the core having a constant total core height measured from the first surface of the planar waveguide layer to the tops of the ridges; the ridge width is less than the total core height; the ridge height is less than the ridge width; and the thickness of the planar waveguide layer is equal to or less than one-fourth of the total core height.