Optical device with graded index planar lens

A device, comprising:

• an integrated photonics chip;
• an input waveguide on the photonics chip;
• and
• a waveguide core layer on the photonics chip and optically coupled to the input waveguide, the waveguide core layer comprising:
• a graded index planar lens having a first end and a second end, the graded index planar lens including a plurality of lens tapers extending from at least one of the first or second ends in a convex array;
• and
• a waveguide slab that adjoins with the graded index planar lens such that the waveguide slab is in optical communication with the plurality of lens tapers;
• wherein the plurality of lens tapers are configured to adiabatically transition an index of refraction from a first index value, external to the graded index planar lens, to a second index value, internal to the graded index planar lens;
• wherein an effective refractive index at cross-sectional positions along the plurality of lens tapers is determined by a width of each lens taper, such that the effective refractive index has a maximum index value where each lens taper has a maximum width value, and as the width of each lens taper is gradually reduced along a length thereof, the effective refractive index is correspondingly gradually transitioned to a final index value that is less than the maximum index value;
• wherein the gradual transition to the final index value substantially reduces or eliminates reflection and mode mismatch, thereby yielding a higher transmission of light through the waveguide slab with decreased optical power loss, while preserving focusing provided by collimating the light.