OPTICAL COUPLING SCHEME

• US 20180231714A1
• Filed: 04/04/2018
• Published: 08/16/2018
• Est. Priority Date: 10/09/2015
• Status: Active Grant

• Current Assignee: Huawei Technologies Research & Development Belgium NV (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Caliopa N.V. (Huawei Investment & Holding Co., Ltd.)
• Inventors: COLLINS, Tom
• Granted Patent: US 10,459,166 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 6/12002 Three-dimensional structures
• CPC Class Codes: G02B 6/12004 Combinations of two or more optical elements
• CPC Class Codes: G02B 6/1223 high refractive index type, i.e. high-contrast waveguides
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/26 Optical coupling means G02B6/36, G02B6/42 take precedence

Abstract

A waveguide structure for optical coupling is provided. The waveguide structure includes a first waveguide embedded in a cladding of a lower refractive index than the first waveguide, a second waveguide of a higher refractive index than the cladding, and an intermediate waveguide. The first waveguide and the second waveguide are physically arranged at the same side of the intermediate waveguide to establish an optical coupling between the first waveguide and the second waveguide through the intermediate waveguide. The first waveguide material has a refractive index value smaller than or equal to 3.

Claims

1. A waveguide structure for optical coupling, comprising:

a first waveguide embedded in a cladding of a lower refractive index than the first waveguide;

a second waveguide of a higher refractive index than the cladding; and

an intermediate waveguide, wherein the first waveguide and the second waveguide are arranged at the same side of the intermediate waveguide to establish an optical coupling between the first waveguide and the second waveguide through the intermediate waveguide;

wherein the first waveguide material has a refractive index value smaller than or equal to 3.

2. The waveguide structure according to claim 1, wherein the first waveguide and the second waveguide each comprise a tapered end;

wherein the intermediate waveguide comprises two tapered ends;

wherein the tapered end of the first waveguide is arranged to face a first tapered end of the intermediate waveguide for establishing an optical coupling between the first waveguide and the intermediate waveguide; and

wherein a second tapered end of the intermediate waveguide is arranged to face the tapered end of the second waveguide for establishing an optical coupling between the intermediate waveguide and the second waveguide.

3. The waveguide structure according to claim 2, wherein the first waveguide has a thickness in the range of 70 nm to 700 nm, the tapered end of the first waveguide at its thinnest part having a width in the range of 100 nm to 2 μ

m.

4. The waveguide structure according to claim 2, wherein the intermediate waveguide has a thickness in the range of 200 nm to 500 nm, the first tapered end of the intermediate waveguide having a width less than 150 nm, and the second tapered end of the intermediate waveguide having a width in the range of 100 nm to 300 nm.

5. The waveguide structure according to claim 2, wherein the second waveguide has a thickness in the range of 200 nm to 2 μ

m, the tapered end of the second waveguide at its thinnest part having a width in the range of 150 nm to 500 nm.

6. The waveguide structure according to claim 1, wherein the intermediate waveguide is formed using a mono-crystalline layer of a silicon-on-insulator wafer substrate, wherein the first waveguide and the second waveguide are arranged on a side of the intermediate waveguide that is opposite to the side facing the silicon-on-insulator wafer substrate.

7. The waveguide structure according to claim 1, wherein the first waveguide is made of a material with a refractive index of 1.7 or higher.

8. The waveguide structure according to claim 1, wherein the second waveguide is made of a group III-V material or a combination of different III-V materials.

9. The waveguide structure according to claim 1, wherein the second waveguide includes at least one active device.

10. The waveguide structure according to claim 1, wherein the first waveguide is made of a material with a refractive index in the range of 1.7 to 2.5

11. A method for fabricating a waveguide structure for optical coupling, comprising:

forming a silicon-on-insulator wafer substrate;

forming an intermediate waveguide within a thin silicon layer of the silicon-on-insulator wafer substrate;

covering the intermediate waveguide with a cladding and planarizing the cladding;

forming a first waveguide on top of the planarized cladding, wherein the cladding comprises a lower refractive index than the first waveguide material;

annealing the formed first waveguide before and/or after patterning of the first waveguide;

applying an overcladding material for embedding the first waveguide;

locally removing the overcladding material to a thickness less than 200 nm above the intermediate waveguide; and

forming a second waveguide in an area where the overcladding material is removed, wherein the second waveguide comprises a higher refractive index than the overcladding.

12. The method according to claim 11, wherein locally removing the overcladding material comprises locally using the first waveguide material as an etch stop layer before the overcladding material is locally removed.

13. The method according to claim 11, wherein the first waveguide layer is a Low Pressure Chemical Vapor Deposition (LPCVD) silicon nitride layer.

14. The method according to claim 11, wherein the second waveguide is formed using transfer printing.

15. The method according to claim 11, wherein the second waveguide is formed by bonding epitaxial layers of III-V material.

16. The method according to claim 11, wherein a further planarising step to the wafer is applied after the second waveguide has been formed and contacts to any active device formed in the second waveguide layer are then added.