End-face coupling structures underneath a photonic layer

1. A method, comprising:

providing a photonic wafer comprising an electrical layer and a layer disposed on a substrate, wherein the layer comprises at least one optical waveguide that is disposed between the electrical layer and the substrate;

removing a portion of the substrate underneath the at least one optical waveguide; and

forming an end-face coupler, wherein a portion of the end-face coupler is within the removed portion of the substrate, and wherein the end-face coupler is configured to transmit an optical signal to, or receive an optical signal from, an external optical device.

2. The method of claim 1 , further comprising forming through vias through the substrate and the layer.

3. The method of claim 1 , wherein forming the end-face coupler comprises:

depositing a first material underneath the at least one optical waveguide; and

depositing a cladding over the end-face coupler, wherein the first material has a higher index of refraction than the cladding.

4. The method of claim 3 , wherein forming the end-face coupler further comprises patterning and etching the first material to form the end-face coupler.

5. The method of claim 3 , wherein forming the end-face coupler comprises, after depositing the first material:

depositing a plurality of different materials on the first material to form a stack; and

patterning and etching the plurality of different materials to form the end-face coupler.

6. The method of claim 3 , wherein forming the end-face coupler comprises, before planarizing the cladding:

depositing a second material onto the cladding to form a first prong of the end-face coupler, wherein the first material forms a second prong of the end-face coupler; and

depositing the cladding over the second material.

7. The method of claim 1 , wherein the substrate of the wafer comprises a semiconductor layer and a buried oxide layer disposed between the semiconductor layer and the layer, wherein removing the portion of the substrate underneath the at least one optical waveguide comprises removing, from underneath the at least one optical waveguide, a portion of the semiconductor layer and a portion of the buried oxide layer.

8. The method of claim 7 , wherein, after forming the end-face coupler, a second portion of the buried oxide layer is between the end-face coupler and the layer.

9. The method of claim 7 , wherein, after forming the end-face coupler, no portion of the buried oxide layer is between the end-face coupler and the layer.

10. The method of claim 1 , wherein the layer further comprises an optical element positioned between the at least one optical waveguide and the electrical layer.

11. The method of claim 1 , further comprising attaching a top layer of the photonic wafer to a carrier.

12. The method of claim 1 , further comprising thinning the substrate before forming the end-face coupler.

13. An apparatus, comprising:

a photonic wafer comprising an electrical layer and a layer disposed on a substrate, wherein the layer comprises at least one optical waveguide that is disposed between the electrical layer and the substrate; and

an end-face coupler, wherein a portion of the end-face coupler is within a portion of the substrate underneath the at least one optical waveguide, and wherein the end-face coupler is configured to direct an optical signal to or from the optical waveguide and comprises an optical interface for end-face coupling.

14. The apparatus of claim 13 , further comprising through vias through the substrate, through the layer, and to the electrical layer.

15. The apparatus of claim 13 , further comprising a cladding disposed around the end-face coupler, wherein the end-face coupler comprises a first material that has a higher index of refraction than the cladding.

16. The apparatus of claim 15 , wherein the end-face coupler further comprises a stack on the first material, the stack comprising a plurality of different materials.

17. The apparatus of claim 15 , wherein the end-face coupler further comprises:

a first prong in the cladding, the first prong comprising a second material; and

a second prong formed by the first material.