PHOTONIC INTEGRATED CIRCUIT HAVING A WAVEGUIDE-GRATING COUPLER

• US 20110150386A1
• Filed: 12/17/2009
• Published: 06/23/2011
• Est. Priority Date: 12/17/2009
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Inventors: Dupuis, Nicolas, Doerr, Christopher R.
• Granted Patent: US 8,494,315 B2
• Time in Patent Office: Days
• US Class Current: 385/14
• 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. An apparatus, comprising:

a first optical waveguide being supported on a surface of a substrate;

a second optical waveguide being supported over the surface;

an optical coupler being supported over the surface and optically coupling the first and second waveguides; and

a waveguide grating being supported over the surface and being adapted to transfer optical power between one or more waveguide modes of the second waveguide and an optical beam formed by or applied to the waveguide grating, wherein the second waveguide has an offset-transition region for which a core of the second waveguide has an offset distance that gradually changes from a first distance corresponding to the optical coupler to a different second distance.

2. The invention of claim 1, wherein a cladding of the second waveguide comprises a wedge-shaped portion located in the offset-transition region.

3. The invention of claim 1, wherein an index-of-refraction contrast of the second waveguide is greater than an index-of-refraction contrast of the first waveguide.

4. The invention of claim 1, wherein at least one of the core and a cladding of the second waveguide comprises a material that is different from materials in a core and a cladding of the first waveguide.

5. The invention of claim 4, wherein:

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

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

the core of the second waveguide comprises silicon; and

the cladding of the second waveguide comprises silicon oxide.

6. The invention of claim 1, wherein the optical coupler couples the first and second optical waveguides via evanescent fields.

7. The invention of claim 6, wherein the optical coupler has a length that causes optical energy to spatially beat one or more times between the first and second optical waveguides.

8. The invention of claim 1, wherein the core of the second optical waveguide comprises:

a first portion that is substantially parallel to a principal plane of the substrate;

a second portion located in the offset-transition region; and

a third portion that is substantially parallel to the principal plane, wherein;

the second portion is connected between the first and third portions; and

the waveguide grating is defined in the third portion.

9. The invention of claim 1, wherein the second offset distance is such that the apparatus produces constructive interference between (i) light diffracted by the waveguide grating toward an interface between a cladding of the first optical waveguide and a cladding of the second optical waveguide and then reflected back by the interface and (ii) light diffracted by the waveguide grating in a direction collinear with a propagation direction of the reflected light.

10. The invention of claim 1, wherein:

a core of first waveguide has a third offset distance with respect to the substrate; and

the third offset distance is outside the range between the first distance and the second distance.

11. The invention of claim 1, wherein a core of the first waveguide comprises a laterally tapered portion connected to the optical coupler.

12. The invention of claim 1, further comprising an optical signal-processing (OSP) circuit supported on the substrate, wherein the first waveguide is optically coupled to the OSP circuit.

13. The invention of claim 12, wherein the OSP circuit comprises at least one active optical element.

14. The invention of claim 12, wherein the first and second waveguides, the waveguide grating, and the OSP circuit are parts of a photonic integrated circuit (PIC) formed on the substrate.

15. The invention of claim 1, wherein the substrate forms a cladding of the first waveguide.

16. A photonic integrated circuit (PIC), comprising:

a substrate;

an optical signal-processing (OSP) circuit being supported on the substrate and having at least one active optical element;

a first optical waveguide being optically coupled to the active optical element;

a second optical waveguide having a waveguide grating adapted to transfer optical power between one or more waveguide modes of the second optical waveguide and an optical beam formed by or applied to the waveguide grating; and

an optical coupler that couples the first and second waveguides via evanescent fields, wherein the second optical waveguide has an offset-transition region, within which a core of the second optical waveguide has an offset distance with respect to the substrate that gradually changes from a first distance to a different second distance.

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

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

18. The invention of claim 17, wherein the step of providing comprises:

forming a layer of cladding material over the first optical waveguide; and

subjecting the layer to a wet-etch process to form from the layer the wedge-like portion.

19. The invention of claim 17, 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;

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;

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

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

the core of the second waveguide comprises silicon; and

the wedge-like portion comprises silicon oxide.

20. The invention of claim 17, wherein, for a specified 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 wavelength diffracted by the waveguide grating toward the interface and then reflected back by the interface and (ii) light of said wavelength diffracted by the waveguide grating in a direction collinear with a propagation direction of the reflected light.