Edge couplers with a partially-etched inverse taper
Structures including an edge coupler and methods of fabricating a structure including an edge coupler. The edge coupler includes a waveguide core having an end surface and a tapered section that terminates at the end surface. The tapered section of the waveguide core includes a slab layer and a ridge layer on the slab layer. The slab layer and the ridge layer each terminate at the end surface. The slab layer has a first width dimension with a first width at a given location along a longitudinal axis of the waveguide core, the ridge layer has a second width dimension with a second width at the given location along the longitudinal axis of the waveguide core, and the first width is greater than the second width.
1. A structure for a photonics chip, the structure comprising:
an edge coupler including a waveguide core comprising single-crystal silicon, the waveguide core having a longitudinal axis, an end surface, a tapered section, and a non-tapered section adjoined to the tapered section, the tapered section and the non-tapered section positioned along the longitudinal axis with the tapered section between the non-tapered section and the end surface, the tapered section including a first slab layer and a ridge layer on the first slab layer, the first slab layer and the ridge layer each terminating at the end surface, the first slab layer having a first width dimension with a first width at a given location along the longitudinal axis of the waveguide core, the ridge layer having a second width dimension with a second width at the given location along the longitudinal axis of the waveguide core, and the first width greater than the second width; and
a laser positioned adjacent to the end surface of the waveguide core,
wherein the first width dimension of the first slab layer in the tapered section increases with increasing distance from the end surface, and the second width dimension of the ridge layer in the tapered section increases with increasing distance from the end surface.
2. The structure of claim 1 wherein the first slab layer and the ridge layer have equal taper angles in the tapered section.
3. The structure of claim 1 wherein the first slab layer and the ridge layer have unequal taper angles in the tapered section.
4. The structure of claim 1 wherein the ridge layer has a first taper angle in the tapered section, the first slab layer has a second taper angle in the tapered section, and the second taper angle is greater than the first taper angle.
5. The structure of claim 1 wherein the ridge layer includes a first plurality of taper angles in different portions of the tapered section, and the ridge layer includes a second plurality of taper angles in different portions of the tapered section.
6. The structure of claim 1 wherein the tapered section and the non-tapered section each include the first slab layer and the ridge layer.
7. The structure of claim 1 wherein the first slab layer and the ridge layer extend along a full length of the tapered section from the end surface to a transition with the non-tapered section.
8. The structure of claim 1 wherein the ridge layer has a first length along the longitudinal axis in the tapered section, the first slab layer has a second length along the longitudinal axis in the tapered section, and the second length is equal to the first length.
9. The structure of claim 1 further comprising:
a substrate including a dielectric layer,
wherein the waveguide core is positioned on the dielectric layer.
10. The structure of claim 1 wherein the tapered section of the waveguide core includes a second slab layer positioned between the ridge layer and the first slab layer, the second slab layer terminates at the end surface, and the second slab layer has a third width dimension that is greater than the second width dimension and less than the first width dimension.
11. The structure of claim 1 wherein the laser and the edge coupler are located on the photonics chip.
12. The structure of claim 1 wherein the laser comprises III-V compound semiconductor materials.
13. The structure of claim 9 wherein the laser is attached to the substrate.
14. A method of forming a structure for a photonics chip, the method comprising:
forming an edge coupler having a waveguide core that includes a longitudinal axis, an end surface, a tapered section, and a non-tapered section adjoined to the tapered section, wherein the tapered section and the non-tapered section are positioned along the longitudinal axis with the tapered section between the non-tapered section and the end surface; and
positioning a laser adjacent to the end surface of the waveguide core,
wherein the waveguide core comprises single-crystal silicon, the tapered section of the waveguide core includes a slab layer and a ridge layer on the slab layer, the slab layer and the ridge layer each terminate at the end surface, the slab layer has a first width dimension with a first width at a given location along the longitudinal axis of the waveguide core, the ridge layer has a second width dimension with a second width at the given location along the longitudinal axis of the waveguide core, the first width dimension of the slab layer in the tapered section increases with increasing distance from the end surface, and the second width dimension of the ridge layer in the tapered section increases with increasing distance from the end surface, and the first width is greater than the second width.
15. The method of claim 14 wherein the slab layer and the ridge layer are patterned by multiple lithography and etching processes.