Compact dual polarization couplers for multi-core optical fibers

An optical device for coupling a multi-core optical fiber to a photonic device comprising:

• a substrate;
• a polarization splitting grating disposed on the substrate, the polarization splitting grating directing light of a first polarization mode in a first propagation direction towards a first side of the polarization splitting grating and light of a second polarization mode in second propagation direction towards a second side of the polarization splitting grating, wherein the first and second sides are greater than or equal to 10 μm and less than or equal to 15 μm in length;
• and
• first and second mode converters extending from the first and second sides of the polarization splitting grating, the first and second mode converters directing the first and second polarization modes in the first and second propagation directions into first and second waveguides extending from the first and second mode converters, respectively, wherein the first and second mode converters comprise lengths along the first and second propagation directions that are less than or equal to the lengths of the first and second sides of the polarization splitting grating, wherein the first mode converter and the second mode converter each comprise a plurality of nanostructures extending along curved contours, the curved contours extending toward a respective waveguide extending from the respective first mode converter or second mode converter.

A method of coupling light from a multi-core optical fiber to a photonic integrated circuit, the method comprising:

• transmitting a plurality of optical signals from a plurality of cores of the multi-core optical fiber onto a grating array of the photonic integrated circuit, the grating array comprising a plurality of polarization splitting gratings disposed on a substrate, the plurality of polarization splitting gratings arranged in a manner that corresponds to the plurality of cores in the multi-core optical fiber to receive one of the optical signals;
• scattering light of each of the plurality of optical signals with one of the plurality of polarization splitting gratings such that first polarization modes and second polarization modes of the plurality of optical signals are directed in first and second propagation directions, respectively;
• individually directing each of the first polarization modes and the second polarization modes into a plurality of waveguides using mode converters extending from each of the plurality of polarization splitting gratings, wherein:
• the multi-core optical fiber comprises at least 5 cores such that at least 10 different polarization modes are directed into the plurality of waveguides via the mode converters;
• and
• adjacent ones of the plurality of cores are separated by a core-to-core separation distance that is less than or equal to 45 μm,
• wherein the mode converters extending from each of the plurality of polarization splitting gratings comprise a plurality of nanostructures extending along curved contours, the curved contours extending toward a waveguide of the plurality of waveguides extending from each of the respective mode converters.