Modal rotation in optical waveguides

A method comprising:

• coupling, with a nanotaper of an optical waveguide structure, a first optical signal and a second optical signal from an external source, the first and second optical signals being coupled as a pair of orthogonally polarized optical signals;
• confining to the optical waveguide structure, with the nanotaper, the first optical signal polarized in a transverse electric (TE) mode and the second optical signal polarized in a transverse magnetic (TM) mode;
• rotating, with a rotator of the optical waveguide structure, the second optical signal from being polarized in the TM mode to being polarized in the TE mode as the second optical signal propagates through the rotator, while maintaining the polarization of the first optical signal polarized in the TE mode;
• receiving, with a separator of the optical waveguide structure, the first optical signal polarized in the TE mode and the second optical signal polarized in the TE mode;
• and
• separating, with the separator of the optical waveguide structure, the first optical signal from the second optical signal into separate first and second waveguide paths.

An apparatus comprising:

• an optical integrated circuit comprising a front-end dielectric optical waveguide structure, the optical waveguide structure configured to at least one of:
• receive a first pair of orthogonally polarized optical signals from an external source and provide the first pair of optical signals as a pair of transverse electric (TE) mode optical signals to processing circuitry;
• or
• receive a second pair of optical signals as a pair of TE mode optical signals and convert the second pair of optical signals to a pair of orthogonally polarized signals for coupling external to the apparatus,
• wherein the optical waveguide structure comprises a dual-layer dielectric core disposed on a substrate,
• wherein a first layer of the dual-layer core comprises a base portion that increases in width from a first end to a second end, and wherein a second layer of the dual-layer core comprises a rib portion that extends over at least a portion of the base portion, the rib portion having a width that is less than the width of the base portion at the first end and at the second end.