Photonic integrated circuit having a waveguide-grating coupler

• US 8,750,654 B2
• Filed: 06/17/2013
• Issued: 06/10/2014
• Est. Priority Date: 12/17/2009
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Inventors: Doerr, Christopher R., Dupuis, Nicolas
• Primary Examiner(s): Le, Uyen Chau N
• Assistant Examiner(s): TRAN, HOANG Q
• Application Number:
  US13/919,396
• Publication Number:
  US 20130277331A1
• Time in Patent Office: 358 Days
• Field of Search: 385/14
• US Class Current: 385/12
• CPC Class Codes: B29D 11/00663 Production of light guides
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/10 of the optical waveguide type G02B6/02, G02B6/24 take precedence; devices or arrangements for the control of light by electric, magnetic, electro-magnetic or acoustic means G02F1/00; transferring the modulation of modulated light G02F2/00; optical logic elements G02F3/00; optical analogue/digital converters G02F7/00
• CPC Class Codes: G02B 6/12002 Three-dimensional structures
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/125 Bends, branchings or intersections
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G02B 6/29332 Wavelength selective couplers, i.e. based on evanescent coupling between light guides, e.g. fused fibre couplers with transverse coupling between fibres having different propagation constant wavelength dependency non wavelength-selective light guide couplers G02B6/28
• CPC Class Codes: G02B 6/305 and having an integrated mode-size expanding section, e.g. tapered waveguide
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• CPC Class Codes: G11B 5/314 where the layers are extra layers normally not provided in the transducing structure, e.g. optical layers G11B5/3196 takes precedence

Abstract

A photonic integrated circuit (PIC) having a waveguide-grating coupler with two evanescently coupled waveguides. The first waveguide is fabricated using materials suitable for manufacturing active optical elements in the PIC. The second waveguide is fabricated using materials capable of providing a relatively high index-of-refraction contrast for the constituent waveguide grating. The waveguide-grating coupler is compatible with the III-V semiconductor technology while being relatively easy to fabricate on an industrial scale.

Claims

1. A method of fabricating an optical device, comprising:

providing a substrate having a first optical waveguide thereon, the first optical waveguide having a first cladding layer;

forming a second cladding layer with a wedge-like portion on the first cladding layer by (i) forming a layer of cladding material over the first optical waveguide and (ii) subjecting said layer of cladding material to a wet-etch process to form from said layer of cladding material the wedge-like portion;

forming a core of a second optical waveguide on the wedge-like portion; and

forming an array of cavities in the core of the second optical waveguide to define therein a waveguide grating.

2. The method of claim 1, further comprising forming on the substrate an optical signal-processing (OSP) circuit, wherein:

the first optical waveguide is optically coupled to the OSP circuit;

the OSP circuit comprises at least one active optical element; and

the first and second optical waveguides, the waveguide grating, and the OSP circuit are parts of a photonic integrated circuit (PIC) formed on the substrate.

3. The method of claim 1, wherein, for a predetermined operating wavelength, an offset distance between the waveguide grating and an interface of a cladding of the first optical waveguide with a cladding of the second waveguide is selected to cause constructive interference between (i) light of said operating wavelength diffracted by the waveguide grating toward the interface and then reflected back by the interface and (ii) light of said operating wavelength diffracted by the waveguide grating in a direction collinear with a propagation direction of the reflected light.

4. The method of claim 1, wherein

a core of the first optical waveguide comprises a ternary, quaternary, or quinary group III-V alloy;

the first cladding layer comprises a binary group III-V compound;

the core of the second waveguide comprises silicon; and

the wedge-like portion comprises silicon oxide.

5. The method of claim 1, further comprising forming a multilayered structure having the substrate, a core of the first optical waveguide, the first cladding layer, the second cladding layer, the core of the second optical waveguide, and a third cladding layer by:

depositing or growing a first core layer on the substrate;

patterning and etching the first core layer in accordance with a footprint layout of the first optical waveguide to form the core of the first optical waveguide;

depositing or growing the first cladding layer over the core of the first optical waveguide and the substrate;

said forming the second cladding layer with the wedge-like portion on the first cladding layer;

depositing or growing a second core layer over the first cladding layer and the second cladding layer with the wedge-like portion;

patterning and etching the second core layer in accordance with a footprint layout of the second optical waveguide to form the core of the second optical waveguide;

said forming the array of cavities in the core of the second optical waveguide; and

depositing or growing the third cladding layer over the core of the second optical waveguide, the second cladding layer with the wedge-like portion, and the first cladding layer.

6. The method of claim 5, wherein:

the first cladding layer comprises a first material; and

the second cladding layer comprises a second material different from the first material.

7. The method of claim 6, wherein the substrate comprises a third material different from the first material and from the second material.

8. The method of claim 6, wherein the third cladding layer comprises a third material different from the first and second materials.

9. The method of claim 8, wherein the substrate comprises a fourth material different from the first, second, and third materials.

10. The method of claim 5, wherein said patterning and etching the first core layer comprises forming a laterally tapered portion of the core of the first optical waveguide.

11. The method of claim 5, wherein:

the first core layer is directly connected to the substrate;

the first cladding layer is directly connected to the first core layer;

the second cladding layer is directly connected to the first cladding layer;

the second core layer is directly connected to the second cladding layer; and

the third cladding layer is directly connected to the second core layer.

12. The method of claim 11, wherein:

a portion of the second core layer is directly connected to the first cladding layer; and

a portion of the third cladding layer is directly connected to the first cladding layer.

13. The method of claim 1, wherein an index-of-refraction contrast of the second optical waveguide is greater than an index-of-refraction contrast of the first optical waveguide.

14. The method of claim 1, wherein the first cladding layer has a thickness that causes the first and second optical waveguides to be optically coupled to each other via an evanescent field.

15. The method of claim 1, further comprising forming a photonic integrated circuit on the substrate, wherein the photonic integrated circuit comprises the first optical waveguide, the second optical waveguide, and the waveguide grating.

16. The method of claim 15, wherein the photonic integrated circuit comprises at least one active optical element.