Optical power splitters with a multiple-level arrangement

1. A structure for an optical power splitter, the structure comprising:

a multimode interference region;

a first dielectric layer over the multimode interference region;

a first waveguide core on the first dielectric layer, the first waveguide core including a portion positioned over the multimode interference region, and the first waveguide core providing a first input port to the optical power splitter;

a second waveguide core on the first dielectric layer, the second waveguide core including a portion positioned over the multimode interference region, and the second waveguide core providing a first output port from the optical power splitter; and

a third waveguide core on the first dielectric layer, the third waveguide core including a portion positioned over the multimode interference region, and the third waveguide core providing a second output port from the optical power splitter,

wherein the multimode interference region is located in a first level, the first waveguide core, the second waveguide core, and the third waveguide core are located in a second level, the second level is positioned in a vertical direction within a different plane than the first level, and the first dielectric layer is positioned as a solid layer between the multimode interference region in the first level and the first waveguide core, the second waveguide core, and the third waveguide core in the second level.

2. The structure of claim 1 wherein the multimode interference region is a slab having a first side surface and a second side surface opposite to the first side surface, the first waveguide core is positioned to extend across the first side surface, and the second waveguide core and the third waveguide core are positioned to extend across the second side surface.

3. The structure of claim 2 wherein the slab includes a tapered section extending from the first side surface, and the portion of the first waveguide core is positioned in part over the tapered section.

4. The structure of claim 2 wherein the portion of the first waveguide core is a tapered section having a terminating end positioned over the slab.

5. The structure of claim 2 wherein the slab includes a first tapered section and a second tapered section extending from the second side surface, the portion of the second waveguide core is positioned in part over the first tapered section, and the portion of the third waveguide core is positioned in part over the second tapered section.

6. The structure of claim 2 wherein the portion of the second waveguide core is a tapered section having a terminating end positioned over the slab, and the portion of the third waveguide core is a tapered section having a terminating end positioned over the slab.

7. The structure of claim 2 wherein the slab includes a tapered section extending from the second side surface, the portion of the second waveguide core and the portion of the third waveguide core are positioned in part over the tapered section.

8. The structure of claim 1 wherein the second waveguide core is positioned adjacent to the third waveguide core, and the portion of the first waveguide core is symmetrically positioned relative to the portion of the second waveguide core and the portion of the third waveguide core.

9. The structure of claim 1 wherein the multimode interference region is comprised of a first material, and the first waveguide core, the second waveguide core, and the third waveguide core are comprised of a second material that differs in composition from the first material.

10. The structure of claim 9 wherein the first material comprises single-crystal silicon, and the second material comprises silicon nitride.

11. The structure of claim 9 further comprising:

a first layer of the second material on the first dielectric layer, the first layer of the second material coupled to a lower portion of the first waveguide core; and

a second layer of the second material on the first dielectric layer, the second layer of the second material coupled to a lower portion of the second waveguide core and a lower portion of the third waveguide core.

12. The structure of claim 1 further comprising:

a fourth waveguide core on the first dielectric layer, the fourth waveguide core including a portion positioned over the multimode interference region, and the fourth waveguide core providing a second input port to the optical power splitter.

13. The structure of claim 12 wherein the multimode interference region is a slab having a side surface, the first waveguide core and the fourth waveguide core are positioned to extend across the side surface, and the portion of the fourth waveguide core is positioned adjacent to the portion of the first waveguide core.

14. The structure of claim 1 wherein the portion of the first waveguide core is a tapered section having a terminating end positioned over the multimode interference region.

15. The structure of claim 1 wherein the portion of the second waveguide core is a tapered section having a terminating end positioned over the multimode interference region, and the portion of the third waveguide core is a tapered section having a terminating end positioned over the multimode interference region.

16. The structure of claim 1 further comprising:

a second dielectric layer positioned as a solid layer between the multimode interference region in the first level and the first waveguide core, the second waveguide core, and the third waveguide core in the second level,

wherein the first dielectric layer and the second dielectric layer comprise different dielectric materials.

17. A method of forming an optical power splitter, the method comprising:

forming a multimode interference region;

forming a dielectric layer over the multimode interference region;

forming a first waveguide core on the dielectric layer, wherein the first waveguide core includes a portion positioned over the multimode interference region, and the first waveguide core provides an input port to the optical power splitter;

forming a second waveguide core on the dielectric layer, wherein the second waveguide includes a portion positioned over the multimode interference region, and the second waveguide core provides a first output port from the optical power splitter; and

forming a third waveguide core on the dielectric layer, wherein the third waveguide core includes a portion positioned over the multimode interference region, and the third waveguide core provides a second output port from the optical power splitter,

wherein the multimode interference region is located in a first level, the first waveguide core, the second waveguide core, and the third waveguide core are located in a second level, the second level is positioned in a vertical direction within a different plane than the first level, and the dielectric layer is positioned as a solid layer between the multimode interference region in the first level and the first waveguide core, the second waveguide core, and the third waveguide core in the second level.

18. The method of claim 17 wherein the multimode interference region is a slab having a first side surface and a second side surface opposite to the first side surface, the first waveguide core is positioned to extend across the first side surface, the second waveguide core is positioned adjacent to the third waveguide core, and the second waveguide core and the third waveguide core are positioned to extend across the second side surface.

19. The method of claim 17 wherein the multimode interference region is comprised of a first material, and the first waveguide core, the second waveguide core, and the third waveguide core are comprised of a second material that differs in composition from the first material.

20. The method of claim 17 wherein the portion of the first waveguide core is a tapered section having a terminating end positioned over the multimode interference region, the portion of the second waveguide core is a tapered section having a terminating end positioned over the multimode interference region, and the portion of the third waveguide core is a tapered section having a terminating end positioned over the multimode interference region.