Two-dimensional grating coupler and methods of making same

A two-dimensional (2D) grating coupler, comprising:

• a planar layer;
• a grating region comprising an array of scattering elements arranged in the planar layer to form a 2D grating;
• a first taper structure in the planar layer connecting a first side of the grating region to a first waveguide, wherein a shape of the first taper structure is a first triangle that is asymmetric about any line perpendicular to the first side of the grating region in the planar layer;
• and
• a second taper structure in the planar layer connecting a second side of the grating region to a second waveguide, wherein a shape of the second taper structure is a second triangle that is asymmetric about any line perpendicular to the second side of the grating region in the planar layer, wherein the first side and the second side are substantially perpendicular to each other such that each of the first taper structure and the second taper structure has a shape and dimensions to reduce light power loss due to light transmission and reflection with respect to the 2D grating, wherein:
• the array of scattering elements are evenly distributed in the planar layer such that there is a same distance between centers of every two adjacent scattering elements along either a first direction perpendicular to the first side of the grating region or a second direction perpendicular to the second side of the grating region,
• the first triangle has a first base side residing on the first side of the grating region, has a first vertex opposite to the first base side, and has a first length along the first direction, and
• the first vertex has a first distance to a perpendicular bisector of the first base side in the planar layer,
• the second triangle has a second base side residing on the second side of the grating region, has a second vertex opposite to the second base side, and has a second length along the second direction,
• the second vertex has a second distance to a perpendicular bisector of the second base side in the planar layer,
• the first distance and the second distance are equal to each other,
• the first taper structure is configured for transmitting a first portion of the incident light to the first waveguide to achieve a minimum insertion loss, and
• the second taper structure is configured for transmitting a second portion of the incident light to the second waveguide to achieve a minimum insertion loss, wherein the first portion of the incident light is substantially a parallel polarization component of the incident light, and the second portion of the incident light is substantially an orthogonal polarization component of the incident light.

An apparatus for optical coupling, comprising:

• a planar layer;
• a grating region comprising an array of scattering elements arranged in the planar layer to form a two-dimensional (2D) grating;
• a first taper structure formed in the planar layer connecting a first side of the grating region to a first waveguide, wherein a shape of the first taper structure is a first triangle that is asymmetric about any line perpendicular to the first side of the grating region in the planar layer;
• and
• a second taper structure formed in the planar layer connecting a second side of the grating region to a second waveguide, wherein a shape of the second taper structure is a second triangle that is asymmetric about any line perpendicular to the second side of the grating region in the planar layer, wherein the first side and the second side are substantially perpendicular to each other, wherein:
• the array of scattering elements are evenly distributed in the planar layer such that there is a same distance between centers of every two adjacent scattering elements along either a first direction perpendicular to the first side of the grating region or a second direction perpendicular to the second side of the grating region,
• the first triangle has a first base side residing on the first side of the grating region, has a first vertex opposite to the first base side, and has a first length along the first direction, and
• the first vertex has a first distance to a perpendicular bisector of the first base side in the planar layer,
• the second triangle has a second base side residing on the second side of the grating region, has a second vertex opposite to the second base side, and has a second length along the second direction,
• the second vertex has a second distance to a perpendicular bisector of the second base side in the planar layer,
• the first distance and the second distance are equal to each other,
• the 2D grating is configured for receiving an incident light from an optical fiber with an incident angle that is non-zero,
• the incident angle is measured in plane of incidence between an axis of the optical fiber and a direction perpendicular to the planar layer, and
• the first length, the second length, the first distance and the second distance are determined based on the incident angle and a position of the optical fiber relative to the 2D grating.