Grating couplers and methods of making same
Disclosed are grating couplers having a high coupling efficiency for optical communications. In one embodiment, an apparatus for optical coupling is disclosed. The apparatus includes: a substrate; a grating coupler comprising a plurality of coupling gratings over the substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section having a middle-raised shape in a second lateral direction, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane; and a cladding layer comprising an optical medium, wherein the cladding layer is filled in over the grating coupler.
1. An apparatus for optical coupling, comprising:
a substrate;
a grating coupler comprising a plurality of coupling gratings over the substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section having a middle-raised shape in a second lateral direction, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane, the grating coupler is configured for receiving optical signals from an optical fiber array at a non-zero angle, and the non-zero angle is measured between an axis of the optical fiber array and a direction perpendicular to the grating plane; and
a cladding layer comprising an optical medium, wherein the cladding layer is filled in over the grating coupler.
2. The apparatus of claim 1 , wherein:
the middle-raised shape is symmetric about a direction perpendicular to the grating plane.
3. The apparatus of claim 1 , wherein:
the middle-raised shape comprises at least three layers.
4. The apparatus of claim 1 , wherein:
the non-zero angle is between 0 and about 15 degrees.
5. The apparatus of claim 1 , wherein:
the grating coupler comprises silicon and silicon oxide; and
the silicon in the grating coupler has a thickness between about 250 and about 350 nanometers.
6. The apparatus of claim 1 , wherein each of the plurality of coupling gratings has a cross-section comprising a first layer disposed on the substrate and a second layer on a middle portion of the first layer, wherein the second layers of the plurality of coupling gratings have duty cycles changing along the second lateral direction.
7. The apparatus of claim 6 , wherein the second layers of the plurality of coupling gratings have duty cycles increasing along the second lateral direction.
8. The apparatus of claim 6 , wherein the second layers of the plurality of coupling gratings have duty cycles decreasing along the second lateral direction.
9. The apparatus of claim 6 , wherein the second layers of the plurality of coupling gratings have duty cycles that first increases and then decreases along the second lateral direction.
10. The apparatus of claim 6 , wherein the second layers of the plurality of coupling gratings have duty cycles that first decreases and then increases along the second lateral direction.
11. The apparatus of claim 6 , wherein the second layers of the plurality of coupling gratings have duty cycles between about 20% and about 50%.
12. The apparatus of claim 6 , wherein the first layers of the plurality of coupling gratings have duty cycles changing along the second lateral direction.
13. An apparatus for optical coupling, comprising:
a substrate;
a grating coupler comprising a plurality of coupling gratings over the substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section having a middle-raised shape in a second lateral direction, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane, and wherein the grating coupler comprises silicon and silicon oxide, and the silicon in the grating coupler has a thickness between about 250 and about 350 nanometers; and
a cladding layer comprising an optical medium, wherein the cladding layer is filled in over the grating coupler.
14. The apparatus of claim 13 , wherein the middle-raised shape is symmetric about a direction perpendicular to the grating plane.
15. The apparatus of claim 13 , wherein the middle-raised shape comprises at least three layers.
16. The apparatus of claim 13 , wherein the grating coupler is configured for receiving optical signals from an optical fiber array at a non-zero angle, wherein the non-zero angle is measured between an axis of the optical fiber array and a direction perpendicular to the grating plane.
17. The apparatus of claim 16 , wherein the non-zero angle is between 0 and about 15 degrees.
18. An apparatus for optical coupling, comprising:
a substrate;
a grating coupler comprising a plurality of coupling gratings over the substrate, wherein each of the plurality of coupling gratings extends in a first lateral direction and has a cross-section in a second lateral direction, wherein the first and second lateral directions are parallel to a surface of the substrate and perpendicular to each other in a grating plane, the grating coupler is configured for receiving optical signals from an optical fiber array at a non-zero angle, and the non-zero angle is measured between an axis of the optical fiber array and a direction perpendicular to the grating plane,
wherein each of the plurality of coupling gratings has a cross-section comprising a first layer disposed on the substrate and a second layer on a middle portion of the first layer,
wherein each of the first and second layers of the plurality of coupling gratings have duty cycles changing along the second lateral direction; and
a cladding layer comprising an optical medium, wherein the cladding layer is filled in over the grating coupler.
19. The apparatus of claim 18 , wherein:
the grating coupler comprises silicon and silicon oxide; and
the silicon in the grating coupler has a thickness between about 250 and about 350 nanometers.
20. The apparatus of claim 18 , wherein the second layers of the plurality of coupling gratings have duty cycles between about 20% and about 50%.