Patent ID: 8160405

Claim:
An apparatus, comprising: a substrate; a first waveguide portion provided on the substrate and configured to receive an optical signal having a first polarization; a second waveguide portion having a length and being provided on the substrate, the optical signal propagating in the second waveguide in a first direction, the first waveguide portion supplying the optical signal to the second waveguide portion, the second waveguide portion having first and second eigen modes oriented along second and third polarizations, respectively, the second waveguide having a first part and a second part that is provided between the first part and the substrate, the first part having a first height and width that is substantially uniform along the length of the second waveguide and second part having second height and width that is substantially uniform along the length of the second waveguide, the second width being greater than the first width, the first width also being uniform in a second direction transverse to the first direction and the second width also being uniform in the second direction; and a third waveguide portion provided on the substrate, the third waveguide portion receiving the optical signal from the second waveguide portion, wherein the second waveguide portion has a first mode index associated with the second polarization and a second mode index associated with the third polarization, such that the second and third polarizations rotate over the length of the second waveguide portion, and the optical signal has a fourth polarization, different than the first polarization, in the third waveguide portion.