Multi-layer waveguide optical coupler

1. An optical coupler comprising:

a plurality of waveguide core layers formed from a waveguide core material having a first index of refraction, said waveguide core layers being (i) arranged in a stacked relationship one over another, (ii) spaced apart one from another and (iii) extending from a light receiving end of the optical coupler longitudinally through the optical coupler toward a light output end of the optical coupler; and

a cladding formed from a cladding material having a second index of refraction, said second index of refraction being less than the first index of refraction, said cladding material surrounding each of the plurality of waveguide core layers;

wherein light propagating within outer ones of the plurality of waveguide core layers is directed toward an interior one of the plurality of waveguide core layers via evanescent coupling between adjacent ones of the plurality of waveguide core layers; and

wherein the plurality of waveguide core layers comprises:

a central waveguide core layer that extends from the light receiving end to the light output end of the optical coupler;

a pair of outermost waveguide core layers arranged on opposite sides of the central waveguide core layer; and

a pair of intermediate waveguide core layers arranged on opposite sides of the central waveguide core layer and interposed between the outermost waveguide core layers and the central waveguide core layer.

2. The optical coupler of claim 1 , wherein the pair of outermost waveguide core layers and the pair of intermediate waveguide core layers stop short of the light output end of the optical coupler.

3. The optical coupler of claim 2 , wherein the central waveguide core layer has a first width at the light receiving end of the optical coupler and the outermost and intermediate pairs of waveguide core layers have a second width at the light receiving end of the optical coupler, said first and second widths being measured normal to a longitudinal axis of the optical coupler and said first width being greater than the second width.

4. The optical coupler of claim 3 , wherein:

the central waveguide core layer tapers from the first width at the light receiving end of the optical coupler to a third width at the light output end of the optical coupler, said first width being greater than the third width; and

the outermost and intermediate pairs of the waveguide core layers taper from the second width at the light receiving end of the optical coupler to the third width at locations distal from the light receiving end of the optical coupler, said second width being greater than the third width.

5. The optical coupler of claim 1 , wherein each of the pair of intermediate waveguide core layers is discontinuous along its longitudinal direction such that a second portion thereof is offset from a first portion thereof by a gap within which is disposed a portion of the cladding.

6. The optical coupler of claim 1 , wherein the plurality of waveguide core layers includes a first outermost waveguide core layer, a first intermediate waveguide core layer arranged over the first outermost waveguide core layer, the central waveguide core layer arranged over the first intermediate waveguide core layer, a second intermediate waveguide core layer arranged over the central waveguide core layer and a second outermost waveguide core layer arranged over the second intermediate waveguide core layer.

7. The optical coupler of claim 6 , wherein the first intermediate waveguide core layer is spaced apart from the first outermost waveguide core layer by between 6% and 13%, inclusive, of a distance d, the central waveguide core layer is spaced apart from the first intermediate waveguide core layer by between 12% and 26%, inclusive, of the distance d, the second intermediate waveguide core layer is spaced apart from the first outermost waveguide core layer by between 18% and 39%, inclusive, of the distance d, the second outermost waveguide core layer is spaced apart from the first outermost waveguide core layer by between 24% and 52%, inclusive, of the distance d, and the distance d is between 1 μm and 4 μm, inclusive.

8. A photonic device comprising:

a light source having a light emitting end from which light is emitted; and

an optical coupler having a light receiving end facing the light emitting end of the light source to receive light emitted therefrom, said optical coupler having a light output end opposite the light receiving end and including:

a plurality of waveguide core layers formed from a waveguide core material having a first index of refraction, said waveguide core layers being (i) stacked one over another, (ii) spaced apart one from another and (iii) extending from the light receiving end of the optical coupler longitudinally through the optical coupler toward the light output end of the optical coupler; and

a cladding formed from a cladding material having a second index of refraction, said second index of refraction being less than the first index of refraction, said cladding material surrounding each of the plurality of waveguide core layers;

wherein each of at least two of the waveguide core layers is a discontinuous waveguide core that is discontinuous along its longitudinal direction such that a second portion thereof is offset from a first portion thereof by a gap within which is disposed a portion of the cladding and

wherein the plurality of waveguide core layers comprises:

a central waveguide core layer;

a pair of outermost wavequide core layers arranged on opposite sides of the central waveguide core layer; and

a pair of intermediate wavequide core layers arranged on opposite sides of the central wavequide core layer and interposed between the outermost waveguide core layers and the central waveguide core layer; and

wherein the central wavequide core layer extends to the light output end of the optical coupler, while the pair of outermost waveguide core layers and the pair of intermediate wavequide core layers stop short of the light output end of the optical coupler.

9. The photonic device of claim 8 , wherein:

the central waveguide core layer tapers from a first width at the light receiving end of the optical coupler to a third width at the light output end of the optical coupler, said first width being greater than the third width; and

the outermost and intermediate pairs of the waveguide core layers taper from a second width at the light receiving end of the optical coupler to the third width at locations distal from the light receiving end of the optical coupler, said second width being greater than the third width and said first, second and third widths being measured normal to a longitudinal axis of the optical coupler.

10. The photonic device of claim 8 , wherein the at least two discontinuous waveguide cores are the pair of intermediate waveguide core layers each of which is discontinuous along its longitudinal direction such that a second portion thereof is offset from a first portion thereof by a gap within which is disposed a portion of the cladding.

11. The photonic device of claim 8 , wherein:

the plurality of waveguide core layers includes a first outermost waveguide core layer, a first intermediate waveguide core layer arranged over the first outermost waveguide core layer, the central waveguide core layer arranged over the first intermediate waveguide core layer, a second intermediate waveguide core layer arranged over the central waveguide core layer and a second outermost waveguide core layer arranged over the second intermediate waveguide core layer; and

the first intermediate waveguide core layer is spaced apart from the first outermost waveguide core layer by between 6% and 13%, inclusive, of a distance d, the central waveguide core layer is spaced apart from the first intermediate waveguide core layer by between 12% and 26%, inclusive, of the distance d, the second intermediatefourth waveguide core layer is spaced apart from the first outermost waveguide core layer by between 18% and 39%, inclusive, of the distance d, and the second outermost waveguide core layer is spaced apart from the first outermost waveguide core layer by between 24% and 52%, inclusive, of the distance d.

12. The photonic device of claim 11 , wherein the distance d is between 1 μm and 4 μm, inclusive.

13. The photonic device of claim 8 , wherein the light source is a laser diode and the light emitted from the light emitting end of the light source has a wavelength in a range of between 1260 nm and 1360 nm, inclusive.

14. The photonic device of claim 8 , wherein the light emitting end of the light source and the light receiving end of the optical coupler are separated by a gap, said gap being filled with a filler material having an index of refraction in a range of between 1.1 and 3.9 inclusive, said filler material being one of a high dielectric constant material and sol-gel.

15. The photonic device of claim 8 , wherein the waveguide core material is silicon nitride and the cladding material is silicon dioxide.

16. A method of fabricating an optical coupler having a first light receiving end and a second light output end opposite the first light receiving end, said method comprising:

forming a cladding from a cladding material having a first index of refraction; and

forming a plurality of waveguide core layers contained within the cladding from a core material having a second index of refraction greater than the first index of refraction, said waveguide core layers being (i) stacked one over another, (ii) spaced apart one from another and (iii) extending from the first light receiving end of the optical coupler longitudinally through the cladding toward the second light output end of the optical coupler;

wherein said plurality of waveguide core layers are arranged such that light energy associated with light that enters outer ones of the plurality of waveguide core layers at the first light receiving end of the optical coupler is conveyed toward an interior one of the plurality of waveguide core layers via evanescent coupling between adjacent ones of the plurality of waveguide core layers; and

wherein the plurality of waveguide core layers comprises:

a central waveguide core layer that extends from the light receiving end to the light output end of the optical coupler;

a pair of outermost waveguide core layers arranged on opposite sides of the central waveguide core layer; and

a pair of intermediate waveguide core layers arranged on opposite sides of the central waveguide core layer and interposed between the outermost waveguide core layers and the central waveguide core layer.

17. The method of claim 16 , wherein:

the core material is silicon nitride; and

the cladding material is silicon dioxide.

18. The method of claim 16 , wherein the pair of outermost waveguide core layers and the pair of intermediate waveguide core layers stop short of the light output end of the optical coupler.

19. The method of claim 18 , wherein the central waveguide core layer has a first width at the light receiving end of the optical coupler and the outermost and intermediate pairs of waveguide core layers have a second width at the light receiving end of the optical coupler, said first and second widths being measured normal to a longitudinal axis of the optical coupler and said first width being greater than the second width.

20. The method of claim 16 , wherein each of the pair of intermediate waveguide core layers is discontinuous along its longitudinal direction such that a second portion thereof is offset from a first portion thereof by a gap within which is disposed a portion of the cladding.