Electro-optical modulators with folded gate layers

• US 9,360,688 B2
• Filed: 04/28/2014
• Issued: 06/07/2016
• 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: Patel, Vipulkumar, Gothoskar, Prakash, Anderson, Sean
• Primary Examiner(s): Radkowski, Peter
• Application Number:
  US14/263,389
• Publication Number:
  US 20150212344A1
• Time in Patent Office: 771 Days
• Field of Search: 385/2, 997/834, 438/31
• 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. In one embodiment, the lower waveguide may include a u-shaped region within an optical mode of the light passing through the optical modulator. By conforming the dielectric layer to the surfaces of the u-shaped region, the amount of area of the dielectric layer within a charge modulation region is increased relative to forming the dielectric layer on a single plane. Folding the dielectric layer in this manner may improve modulation efficiency. In one embodiment, the u-shaped region is formed by using ridge structures that extend from an upper surface of the lower waveguide towards the upper waveguide. To aid in lateral confinement of the optical mode, the dielectric layer may be deposited on one side surface of the ridge structures while a different dielectric material is deposited on the opposite side surface.

Claims

1. An optical device comprising:

a first silicon waveguide comprising at least three ridge structures extending from an upper surface of the first silicon waveguide, the ridge structures defining at least two U-shaped regions on the upper surface;

a dielectric layer disposed conformally on the upper surface in the two U-shaped regions; and

a second silicon waveguide disposed conformally on a first surface of the dielectric layer opposite a second surface of the dielectric layer contacting the upper surface, wherein respective portions of the second silicon waveguide are disposed within the U-shaped regions,

wherein the first silicon waveguide is doped a first conductivity type and the second silicon waveguide is doped a second, different conductivity type,

wherein the second silicon waveguide includes a ridge portion extending away from an upper surface of the second silicon waveguide opposite a lower surface of the second silicon waveguide contacting the dielectric layer, wherein at least of one of the U-shaped regions and the ridge portion are disposed along an axis perpendicular to the upper surface of the first waveguide.

2. The optical device of claim 1, wherein a distance between the ridge structures forming each of the two U-shaped regions is less than half a micron.

3. The optical device of claim 1, wherein at least one of the ridge structures is between two outer ridge structures, wherein a dielectric material is disposed along respective sides of the two outer ridge structures facing away from the at least one ridge structure, wherein the dielectric material is different than a material of the dielectric layer.

4. The optical device of claim 1, wherein the first silicon waveguide comprises raised wings, wherein the ridges structures are arranged between the raised wings, and wherein a dielectric material different from a material of the dielectric layer is disposed between the raised wings and the ridge structures.

5. The optical device of claim 4, wherein the raised wings are more heavily doped the first conductivity type than a remaining portion of the first silicon waveguide.

6. The optical device of claim 1, wherein first and second electrical contacts are coupled to a same side of the first silicon waveguide and third and fourth electrical contacts are coupled to a same side of the second silicon waveguide, wherein the first and second electrical contacts are equally spaced from a closest respective ridge structure, wherein the optical device is configured to receive a first voltage at the first and second electrical contacts and a second voltage at the third and fourth electrical contacts to generate a voltage potential that establishes a charge modulation region.

7. The optical device of claim 1, wherein a width of the ridge portion extends between a leftmost edge of a first one of the ridge structures and a rightmost edge of a second one of the ridge structures, wherein the first and second ridge structures form the at least one U-shaped region disposed between the ridge portion and the first waveguide.

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

9. An optical device comprising:

a first waveguide comprising two ridge structures extending from an upper surface of the first waveguide, the two ridge structures defining at least one U-shaped region on the upper surface, wherein a distance between the two ridge structures is less than 100 nanometers;

a dielectric layer disposed conformally on the upper surface in the U-shaped region; and

a second waveguide disposed conformally on a first surface of the dielectric layer opposite a second surface of the dielectric layer contacting the upper surface, wherein a portion of the second waveguide is disposed within the U-shaped region,

wherein the first waveguide is doped a first conductivity type and the second waveguide is doped a second, different conductivity type,

wherein the second silicon waveguide includes a ridge portion extending away from an upper surface of the second silicon waveguide opposite a lower surface of the second silicon waveguide contacting the dielectric layer, wherein the U-shaped region and the ridge portion are disposed along an axis perpendicular to the upper surface of the first waveguide.

10. The optical device of claim 9, wherein the distance between the two ridge structures is between 25 nanometers and 75 nanometers.

11. The optical device of claim 10, wherein a thickness of the lower waveguide in a region excluding the two ridge structures is between 50 nanometers to 200 nanometers.

12. The optical device of claim 9, wherein a dielectric material is disposed along respective sides of the two ridge structures facing away the other ridge structure, wherein the dielectric material is different than a material of the dielectric layer.

13. The optical device of claim 9, wherein a material of the ridge portion is the same as a material of the second waveguide.

14. The optical device of claim 9, wherein the ridge portion is arranged to be between respective planes defined by a leftmost edge of a leftmost ridge structure of the two ridge structures and a rightmost edge of a rightmost ridge structure of the two ridges structures.