Ultralow loss interlayer transition design for integrated multilayer photonic platform

A multicore waveguide, comprising:

• a first lateral interface and a second lateral interface that are perpendicular to a first lateral axis and define a lengthwise dimension of the multicore waveguide;
• a first lateral side and a second lateral side that are perpendicular to a second lateral axis and define a widthwise dimension of the multicore waveguide;
• a cladding layer;
• a first waveguide core arranged in the cladding layer and configured to guide a first optical signal lengthwise along at least a first portion of the multicore waveguide;
• and
• a second waveguide core arranged in the cladding layer and configured to guide a second optical signal lengthwise along at least a second portion of the multicore waveguide,
• wherein the first waveguide core and the second waveguide core are spatially overlapped in a vertical direction in a third portion of the multicore waveguide,
• wherein the first waveguide core and the second waveguide core are optically coupled in the vertical direction to transfer an optical signal between the first waveguide core and the second waveguide core,
• wherein the first waveguide core includes:
• a first constant width section that extends lengthwise, along a first center axis, from the first lateral interface toward the second lateral interface, wherein the first constant width section has a first constant width;
• a first tapered width section that extends lengthwise, along the first center axis, from the first constant width section toward the second lateral interface, wherein the first tapered width section has a first tapered width that tapers from the first constant width section to a first tip section having a first tip width;
• and
• a first displacing waveguide section that extends from the first tip section to the second lateral interface, wherein the first displacing waveguide section has a first displaced waveguide tip, arranged at the second lateral interface, that has a first lateral offset distance from the first center axis,
• wherein the second waveguide core includes:
• a second constant width section that extends lengthwise, along a second center axis, from the second lateral interface toward the first lateral interface, wherein the second constant width section has a second constant width;
• and
• a second tapered width section that extends lengthwise, along the second center axis, from the second constant width section toward the first lateral interface, wherein the second tapered width section has a second tapered width that tapers from the second constant width section to a second tip section having a second tip width.

An interlayer transition coupling structure, comprising:

• a first waveguide mode path configured to propagate a first waveguide mode;
• and
• a second waveguide mode path configured to propagate a second waveguide mode,
• wherein the first waveguide mode path and the second waveguide mode path are partially overlapped and are configured to couple the first waveguide mode and second waveguide mode,
• wherein the first waveguide mode path has a waveguide tip section,
• wherein the first waveguide mode path has a displacement mode path starting at the waveguide tip section, wherein the displacement mode path is gradually displaced from the second waveguide mode path, and
• wherein the displacement mode path is configured to gradually decouple the first waveguide mode from the second waveguide mode or gradually couple the first waveguide mode to the second waveguide mode.