ELECTRO-OPTICAL MODULATOR USING RIBBED WAVEGUIDES

• US 20160170240A1
• Filed: 04/08/2014
• Published: 06/16/2016
• Est. Priority Date: 01/24/2014
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: ADAMS, Donald, GOTHOSKAR, Prakash, PATEL, Vipulkumar, WEBSTER, Mark
• Granted Patent: US 9,766,484 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02B 6/132 by deposition of thin films
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0152 using free carrier effects, e.g. plasma effect
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 1/2257 the optical waveguides being made of semiconducting material
• CPC Class Codes: Y10S 977/834 Optical properties of nanomaterial, e.g. specified transparency, opacity, or index of refraction

Abstract

An optical modulator may include a lower waveguide, an upper waveguide, and a dielectric layer disposed therebetween. When a voltage potential is created between the lower and upper waveguides, these layers form a silicon-insulator-silicon capacitor (also referred to as SISCAP) guide that provides efficient, high-speed optical modulation of an optical signal passing through the modulator. In one embodiment, at least one of the waveguides includes a respective ridge portion aligned at a charge modulation region which may aid in confining the optical mode laterally (e.g., in the width direction) in the optical modulator. In another embodiment, ridge portions may be formed on both the lower and the upper waveguides. These ridge portions may be aligned in a vertical direction (e.g., a thickness direction) so that ridges overlap which may further improve optical efficiency by centering an optical mode in the charge modulation region.

Claims

1. An optical device, comprising:

a first silicon waveguide disposed on a dielectric substrate, the first silicon waveguide comprising a first ridge extending in a direction of an optical path;

a dielectric layer having a lower surface disposed on an upper surface of the first ridge;

a second silicon waveguide disposed on an upper surface of the dielectric layer opposite the lower surface of the dielectric layer, the second silicon waveguide comprising a second ridge extending in a direction of the optical path, wherein the second ridge at least partially overlaps both the dielectric layer and the first ridge, and wherein the first silicon waveguide is doped a first conductivity type and the second silicon waveguide is doped a second, different conductivity type;

a first electrical contact coupled to the first silicon waveguide; and

a second electrical contact coupled to the second silicon waveguide.

2. The optical device of claim 1, wherein respective widths of the first and second ridges in a direction perpendicular to the direction of the optical path are equal.

3. The optical device of claim 2, wherein the second ridge completely overlaps the first ridge.

4. The optical device of claim 1, wherein the first electrical contact and a third electrical contact are coupled to a same side of the first silicon waveguide, wherein the first ridge is centered on the first silicon waveguide in a direction perpendicular to the direction of the optical path and the first ridge is located between the first and third electrical contacts, wherein the first, second, and third electrical contacts are configured to generate a voltage potential that establishes a charge modulation region comprising at least respective portions of the first ridge, the dielectric layer, and the second silicon waveguide.

5. The optical device of claim 1, wherein the first silicon waveguide comprises raised wings, wherein the first ridge is arranged between the raised wings, and wherein a dielectric material is disposed between the raised wings and the first ridge.

6. The optical device of claim 5, wherein the raised wings are more heavily doped the first conductivity type than a remaining portion of the first silicon waveguide, wherein the first electrical contact is coupled to a first one of the raised wings and a third electrical contact is coupled to a second one of the raised wings.

7. The optical device of claim 1, wherein the second silicon waveguide comprises raised wings, wherein the second ridge is arranged between the raised wings, and wherein a dielectric material is disposed between the raised wings and the second ridge.

8. The optical device of claim 1, wherein the second ridge on the second silicon waveguide comprises a different material than a remaining portion of the second silicon waveguide.

9. The optical device of claim 1, wherein the first electrical contact and a third electrical contact are coupled to a same side of the first silicon waveguide, wherein the second electrical contact and a fourth electrical contact are coupled to a same side of the second silicon waveguide, wherein the optical device is configured to receive a first voltage at the first and third electrical contacts and a second voltage at the second and fourth electrical contacts to generate a voltage potential that establishes a charge modulation region.

10. A method for forming an optical device, the method comprising:

forming a first silicon waveguide on a dielectric substrate, the first silicon waveguide comprising a first ridge extending in a direction of an optical path;

forming a dielectric layer on the first ridge;

forming a second silicon waveguide disposed on an upper surface of the dielectric layer opposite a lower surface of the dielectric layer contacting the first ridge, the second silicon waveguide comprising a second ridge extending in a direction of the optical path, wherein the second ridge at least partially overlaps both the dielectric layer and the first ridge, and wherein the first silicon waveguide is doped a first conductivity type and the second silicon waveguide is doped a second, different conductivity type; and

coupling a first electrical contact to the first silicon waveguide; and

coupling a second electrical contact to the second silicon waveguide.

11. The method of claim 10, wherein respective widths of the first and second ridges in a direction perpendicular to the direction of the optical path are equal.

12. The method of claim 10, further comprising, after forming the dielectric layer and before forming the second silicon waveguide:

depositing dielectric material; and

planarizing the dielectric material to expose the upper surface of the dielectric layer, whereby an upper surface of the dielectric material is co-planar with the upper surface of the dielectric layer.

13. The method of claim 10, wherein the first silicon waveguide comprises raised wings, wherein the first ridge is arranged between the raised wings, and wherein a dielectric material is disposed between the raised wings and the first ridge.

14. The method of claim 10, wherein forming the dielectric layer comprises thermally growing the dielectric layer from a material of the first silicon waveguide, wherein the dielectric layer is silicon dioxide.

15. The method of claim 10, wherein the second ridge comprises a different material than a remaining portion of the second silicon waveguide.

16. The method of claim 15, further comprises:

forming a nitride capping layer that surrounds at least three sides of the second silicon waveguide; and

selectively removing a portion of the nitride capping layer to form the second ridge on an upper surface of the second silicon waveguide.

17. An optical device, comprising:

a first waveguide disposed on a substrate, the first waveguide comprising a first ridge extending in a direction of an optical path;

a second waveguide disposed above an upper surface of the first ridge opposite a lower surface of the first waveguide contacting the substrate, the second waveguide comprising a second ridge extending in a direction of the optical path, wherein the second ridge at least partially overlaps the first ridge in a direction perpendicular to the direction of the optical path, and wherein the first waveguide is doped a first conductivity type and the second waveguide is doped a second, different conductivity type;

a first electrical contact coupled to the first waveguide; and

a second electrical contact coupled to the second waveguide.

18. The optical device of claim 17, wherein respective widths of the first and second ridges in a direction perpendicular to the direction of propagation of the optical signal are the same.

19. The optical device of claim 17, wherein the first and second ridges comprise a same material as remaining portions of the first and second waveguides, respectively.

20. The optical device of claim 17, wherein the first ridge comprises a same material as a remaining portion of the first waveguide and the second ridge comprises a different material as a remaining portion of the second waveguide, wherein the different material of the second ridge is a dielectric material.